Skip to content

Getting Started

You can import the necessary types and functions from the effect/Schema module:

Example (Namespace Import)

import * as Schema from "effect/Schema"

Example (Named Import)

import { Schema } from "effect"

One common way to define a Schema is by utilizing the Struct constructor. This constructor allows you to create a new schema that outlines an object with specific properties. Each property in the object is defined by its own schema, which specifies the data type and any validation rules.

Example

Consider the following schema that describes a person object with:

  • a name property of type string
  • an age property of type number
1
import {
import Schema
Schema
} from "effect"
2
3
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
6
})

Once you’ve defined a schema (Schema<Type, Encoded, Context>), you can extract the inferred type Type in two ways:

  1. Using the Schema.Type utility.
  2. Using the Type field defined on your schema.

Example

1
import {
import Schema
Schema
} from "effect"
2
3
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
6
})
7
8
// 1. Using the Schema.Type utility
9
type
type Person = { readonly name: string; readonly age: number; }
Person
=
import Schema
Schema
.
namespace Schema
Schema
.
type Schema<in out A, in out I = A, out R = never>.Type<S> = S extends Schema.Schema.Variance<infer A, infer _I, infer _R> ? A : never
Type
<typeof
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
>
10
11
// 2. Using the `Type` field
12
type
type Person2 = { readonly name: string; readonly age: number; }
Person2
= typeof
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
.
(property) Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>.Type: { readonly name: string; readonly age: number; }
Type

The result is equivalent to:

type Person = {
name: string
age: number
}

Alternatively, you can extract the Person type using the interface keyword.

Example

1
import {
import Schema
Schema
} from "effect"
2
3
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
6
})
7
8
interface
interface Person
Person
extends
import Schema
Schema
.
namespace Schema
Schema
.
type Schema<in out A, in out I = A, out R = never>.Type<S> = S extends Schema.Schema.Variance<infer A, infer _I, infer _R> ? A : never
Type
<typeof
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
> {}

Both approaches yield the same result, but using an interface provides benefits such as performance advantages and improved readability.

In cases where in a Schema<Type, Encoded, Context> the Encoded type differs from the Type type, you can extract the inferred Encoded in two ways:

  1. Using the Schema.Encoded utility.
  2. Using the Encoded field defined on your schema.

Example

1
import {
import Schema
Schema
} from "effect"
2
3
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }>(fields: { name: typeof Schema.String; age: typeof Schema.NumberFromString; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
// a schema that decodes a string to a number
6
(property) age: typeof Schema.NumberFromString
age
:
import Schema
Schema
.
class NumberFromString

This schema transforms a `string` into a `number` by parsing the string using the `parse` function of the `effect/Number` module. It returns an error if the value can't be converted (for example when non-numeric characters are provided). The following special string values are supported: "NaN", "Infinity", "-Infinity".

NumberFromString
7
})
8
9
// 1. Using the Schema.Encoded utility
10
type
type PersonEncoded = { readonly name: string; readonly age: string; }
PersonEncoded
=
import Schema
Schema
.
namespace Schema
Schema
.
type Schema<in out A, in out I = A, out R = never>.Encoded<S> = S extends Schema.Schema.Variance<infer _A, infer I, infer _R> ? I : never
Encoded
<typeof
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }>
Person
>
11
12
// 2. Using the `Encoded` field
13
type
type PersonEncoded2 = { readonly name: string; readonly age: string; }
PersonEncoded2
= typeof
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }>
Person
.
(property) Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: string; }, never>.Encoded: { readonly name: string; readonly age: string; }
Encoded

The result is equivalent to:

type PersonEncoded = {
name: string
age: string
}

Note that age is of type string in the Encoded type of the schema and is of type number in the Type type of the schema.

Alternatively, you can extract the PersonEncoded type using the interface keyword.

Example

1
import {
import Schema
Schema
} from "effect"
2
3
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }>(fields: { name: typeof Schema.String; age: typeof Schema.NumberFromString; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
// a schema that decodes a string to a number
6
(property) age: typeof Schema.NumberFromString
age
:
import Schema
Schema
.
class NumberFromString

This schema transforms a `string` into a `number` by parsing the string using the `parse` function of the `effect/Number` module. It returns an error if the value can't be converted (for example when non-numeric characters are provided). The following special string values are supported: "NaN", "Infinity", "-Infinity".

NumberFromString
7
})
8
9
interface
interface PersonEncoded
PersonEncoded
extends
import Schema
Schema
.
namespace Schema
Schema
.
type Schema<in out A, in out I = A, out R = never>.Encoded<S> = S extends Schema.Schema.Variance<infer _A, infer I, infer _R> ? I : never
Encoded
<typeof
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }>
Person
> {}

Both approaches yield the same result, but using an interface provides benefits such as performance advantages and improved readability.

You can also extract the inferred type Context that represents the context required by the schema.

Example

1
import {
import Schema
Schema
} from "effect"
2
3
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
6
})
7
8
// 1. Using the Schema.Context utility
9
type
type PersonContext = never
PersonContext
=
import Schema
Schema
.
namespace Schema
Schema
.
type Schema<in out A, in out I = A, out R = never>.Context<S> = S extends Schema.Schema.Variance<infer _A, infer _I, infer R> ? R : never
Context
<typeof
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
>
10
11
// 2. Using the `Context` field
12
type
type PersonContext2 = never
PersonContext2
= typeof
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
.
(property) Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>.Context: never
Context

When defining a schema, you may want to create a schema with an opaque type. This is useful when you want to hide the internal structure of the schema and only expose the type of the schema.

Example

To create a schema with an opaque type, you can use the following technique that re-declares the schema:

1
import {
import Schema
Schema
} from "effect"
2
3
const
const _Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
_Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
6
})
7
8
interface
interface Person
Person
extends
import Schema
Schema
.
namespace Schema
Schema
.
type Schema<in out A, in out I = A, out R = never>.Type<S> = S extends Schema.Schema.Variance<infer A, infer _I, infer _R> ? A : never
Type
<typeof
const _Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
_Person
> {}
9
10
// Re-declare the schema to create a schema with an opaque type
11
const
const Person: Schema.Schema<Person, Person, never>
Person
:
import Schema
Schema
.
interface Schema<in out A, in out I = A, out R = never> namespace Schema
Schema
<
interface Person
Person
> =
const _Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
_Person

Alternatively, you can use the Class APIs (see the Class APIs section for more details).

Note that the technique shown above becomes more complex when the schema is defined such that Type is different from Encoded.

Example

1
import {
import Schema
Schema
} from "effect"
2
3
const
const _Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }>
_Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }>(fields: { name: typeof Schema.String; age: typeof Schema.NumberFromString; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
// a schema that decodes a string to a number
6
(property) age: typeof Schema.NumberFromString
age
:
import Schema
Schema
.
class NumberFromString

This schema transforms a `string` into a `number` by parsing the string using the `parse` function of the `effect/Number` module. It returns an error if the value can't be converted (for example when non-numeric characters are provided). The following special string values are supported: "NaN", "Infinity", "-Infinity".

NumberFromString
7
})
8
9
interface
interface Person
Person
extends
import Schema
Schema
.
namespace Schema
Schema
.
type Schema<in out A, in out I = A, out R = never>.Type<S> = S extends Schema.Schema.Variance<infer A, infer _I, infer _R> ? A : never
Type
<typeof
const _Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }>
_Person
> {}
10
11
interface
interface PersonEncoded
PersonEncoded
extends
import Schema
Schema
.
namespace Schema
Schema
.
type Schema<in out A, in out I = A, out R = never>.Encoded<S> = S extends Schema.Schema.Variance<infer _A, infer I, infer _R> ? I : never
Encoded
<typeof
const _Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }>
_Person
> {}
12
13
// Re-declare the schema to create a schema with an opaque type
14
const
const Person: Schema.Schema<Person, PersonEncoded, never>
Person
:
import Schema
Schema
.
interface Schema<in out A, in out I = A, out R = never> namespace Schema
Schema
<
interface Person
Person
,
interface PersonEncoded
PersonEncoded
> =
const _Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.NumberFromString; }>
_Person

In this case, the field "age" is of type string in the Encoded type of the schema and is of type number in the Type type of the schema. Therefore, we need to define two interfaces (PersonEncoded and Person) and use both to redeclare our final schema Person.

It’s important to note that by default, most constructors exported by effect/Schema return readonly types.

Example

For instance, in the Person schema below:

1
import {
import Schema
Schema
} from "effect"
2
3
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
6
})

the resulting inferred Type would be:

{
readonly name: string;
readonly age: number;
}

When working with unknown data types in TypeScript, decoding them into a known structure can be challenging. Luckily, effect/Schema provides several functions to help with this process. Let’s explore how to decode unknown values using these functions.

APIDescription
decodeUnknownSyncSynchronously decodes a value and throws an error if parsing fails.
decodeUnknownOptionDecodes a value and returns an Option type.
decodeUnknownEitherDecodes a value and returns an Either type.
decodeUnknownPromiseDecodes a value and returns a Promise.
decodeUnknownDecodes a value and returns an Effect.

The Schema.decodeUnknownSync function is useful when you want to parse a value and immediately throw an error if the parsing fails.

Example

1
import {
import Schema
Schema
} from "effect"
2
3
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
6
})
7
8
// Simulate an unknown input
9
const
const input: unknown
input
: unknown = {
(property) name: string
name
: "Alice",
(property) age: number
age
: 30 }
10
11
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
import Schema
Schema
.
(alias) decodeUnknownSync<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }>(schema: Schema.Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>, options?: ParseOptions): (u: unknown, overrideOptions?: ParseOptions) => { readonly name: string; readonly age: number; } export decodeUnknownSync
decodeUnknownSync
(
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
)(
const input: unknown
input
))
12
// Output: { name: 'Alice', age: 30 }
13
14
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
import Schema
Schema
.
(alias) decodeUnknownSync<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }>(schema: Schema.Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>, options?: ParseOptions): (u: unknown, overrideOptions?: ParseOptions) => { readonly name: string; readonly age: number; } export decodeUnknownSync
decodeUnknownSync
(
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
)(null))
15
/*
16
throws:
17
ParseError: Expected { readonly name: string; readonly age: number }, actual null
18
*/

The Schema.decodeUnknownEither function returns an Either type representing success or failure.

Example

1
import {
import Schema
Schema
} from "effect"
2
import {
import Either
Either
} from "effect"
3
4
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
5
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
6
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
7
})
8
9
const
const decode: (u: unknown, overrideOptions?: ParseOptions) => Either.Either<{ readonly name: string; readonly age: number; }, ParseError>
decode
=
import Schema
Schema
.
const decodeUnknownEither: <{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }>(schema: Schema.Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>, options?: ParseOptions) => (u: unknown, overrideOptions?: ParseOptions) => Either.Either<...>
decodeUnknownEither
(
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
)
10
11
// Simulate an unknown input
12
const
const input: unknown
input
: unknown = {
(property) name: string
name
: "Alice",
(property) age: number
age
: 30 }
13
14
const
const result1: Either.Either<{ readonly name: string; readonly age: number; }, ParseError>
result1
=
const decode: (u: unknown, overrideOptions?: ParseOptions) => Either.Either<{ readonly name: string; readonly age: number; }, ParseError>
decode
(
const input: unknown
input
)
15
if (
import Either
Either
.
const isRight: <{ readonly name: string; readonly age: number; }, ParseError>(self: Either.Either<{ readonly name: string; readonly age: number; }, ParseError>) => self is Either.Right<...>

Determine if a `Either` is a `Right`.

isRight
(
const result1: Either.Either<{ readonly name: string; readonly age: number; }, ParseError>
result1
)) {
16
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
const result1: Either.Right<ParseError, { readonly name: string; readonly age: number; }>
result1
.
(property) Right<ParseError, { readonly name: string; readonly age: number; }>.right: { readonly name: string; readonly age: number; }
right
)
17
/*
18
Output:
19
{ name: "Alice", age: 30 }
20
*/
21
}
22
23
const
const result2: Either.Either<{ readonly name: string; readonly age: number; }, ParseError>
result2
=
const decode: (u: unknown, overrideOptions?: ParseOptions) => Either.Either<{ readonly name: string; readonly age: number; }, ParseError>
decode
(null)
24
if (
import Either
Either
.
const isLeft: <{ readonly name: string; readonly age: number; }, ParseError>(self: Either.Either<{ readonly name: string; readonly age: number; }, ParseError>) => self is Either.Left<...>

Determine if a `Either` is a `Left`.

isLeft
(
const result2: Either.Either<{ readonly name: string; readonly age: number; }, ParseError>
result2
)) {
25
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
const result2: Either.Left<ParseError, { readonly name: string; readonly age: number; }>
result2
.
(property) Left<ParseError, { readonly name: string; readonly age: number; }>.left: ParseError
left
)
26
/*
27
Output:
28
{
29
_id: 'ParseError',
30
message: 'Expected { readonly name: string; readonly age: number }, actual null'
31
}
32
*/
33
}

If your schema involves asynchronous transformations, the Schema.decodeUnknownSync and Schema.decodeUnknownEither functions will not be suitable. In such cases, you should use the Schema.decodeUnknown function, which returns an Effect.

Example

1
import {
import Schema
Schema
} from "effect"
2
import {
import Effect
Effect
} from "effect"
3
4
const
const PersonId: typeof Schema.Number
PersonId
=
import Schema
Schema
.
(alias) class Number export Number
Number
5
6
const
const Person: Schema.Struct<{ id: typeof Schema.Number; name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ id: typeof Schema.Number; name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { id: typeof Schema.Number; name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<...> (+1 overload) namespace Struct
Struct
({
7
(property) id: typeof Schema.Number
id
:
const PersonId: typeof Schema.Number
PersonId
,
8
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
9
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
10
})
11
12
const
const asyncSchema: Schema.transformOrFail<typeof Schema.Number, Schema.Struct<{ id: typeof Schema.Number; name: typeof Schema.String; age: typeof Schema.Number; }>, never>
asyncSchema
=
import Schema
Schema
.
const transformOrFail: <Schema.Struct<{ id: typeof Schema.Number; name: typeof Schema.String; age: typeof Schema.Number; }>, typeof Schema.Number, never, never>(from: typeof Schema.Number, to: Schema.Struct<...>, options: { ...; } | { ...; }) => Schema.transformOrFail<...> (+1 overload)

Create a new `Schema` by transforming the input and output of an existing `Schema` using the provided decoding functions.

transformOrFail
(
const PersonId: typeof Schema.Number
PersonId
,
const Person: Schema.Struct<{ id: typeof Schema.Number; name: typeof Schema.String; age: typeof Schema.Number; }>
Person
, {
13
(property) strict?: true
strict
: true,
14
// Simulate an async transformation
15
(property) decode: (fromA: number, options: ParseOptions, ast: Transformation, fromI: number) => Effect.Effect<{ readonly id: number; readonly name: string; readonly age: number; }, ParseIssue, never>
decode
: (
(parameter) id: number
id
) =>
16
import Effect
Effect
.
const succeed: <{ id: number; name: string; age: number; }>(value: { id: number; name: string; age: number; }) => Effect.Effect<{ id: number; name: string; age: number; }, never, never>

Creates an `Effect` that succeeds with the provided value. Use this function to represent a successful computation that yields a value of type `A`. The effect does not fail and does not require any environmental context.

succeed
({
(property) id: number
id
,
(property) name: string
name
: "name",
(property) age: number
age
: 18 }).
(method) Pipeable.pipe<Effect.Effect<{ id: number; name: string; age: number; }, never, never>, Effect.Effect<{ id: number; name: string; age: number; }, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<{ id: number; name: string; age: number; }, never, never>) => Effect.Effect<...>): Effect.Effect<...> (+21 overloads)
pipe
(
17
import Effect
Effect
.
const delay: (duration: DurationInput) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, R> (+1 overload)

Returns an effect that is delayed from this effect by the specified `Duration`.

delay
("10 millis")
18
),
19
(property) encode: (toI: { readonly id: number; readonly name: string; readonly age: number; }, options: ParseOptions, ast: Transformation, toA: { ...; }) => Effect.Effect<...>
encode
: (
(parameter) person: { readonly id: number; readonly name: string; readonly age: number; }
person
) =>
20
import Effect
Effect
.
const succeed: <number>(value: number) => Effect.Effect<number, never, never>

Creates an `Effect` that succeeds with the provided value. Use this function to represent a successful computation that yields a value of type `A`. The effect does not fail and does not require any environmental context.

succeed
(
(parameter) person: { readonly id: number; readonly name: string; readonly age: number; }
person
.
(property) id: number
id
).
(method) Pipeable.pipe<Effect.Effect<number, never, never>, Effect.Effect<number, never, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<number, never, never>) => Effect.Effect<number, never, never>): Effect.Effect<...> (+21 overloads)
pipe
(
import Effect
Effect
.
const delay: (duration: DurationInput) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, R> (+1 overload)

Returns an effect that is delayed from this effect by the specified `Duration`.

delay
("10 millis"))
21
})
22
23
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
import Schema
Schema
.
const decodeUnknownEither: <{ readonly id: number; readonly name: string; readonly age: number; }, number>(schema: Schema.Schema<{ readonly id: number; readonly name: string; readonly age: number; }, number, never>, options?: ParseOptions) => (u: unknown, overrideOptions?: ParseOptions) => Either<...>
decodeUnknownEither
(
const asyncSchema: Schema.transformOrFail<typeof Schema.Number, Schema.Struct<{ id: typeof Schema.Number; name: typeof Schema.String; age: typeof Schema.Number; }>, never>
asyncSchema
)(1))
24
/*
25
Output:
26
{
27
_id: 'Either',
28
_tag: 'Left',
29
left: {
30
_id: 'ParseError',
31
message: '(number <-> { readonly id: number; readonly name: string; readonly age: number })\n' +
32
'└─ cannot be be resolved synchronously, this is caused by using runSync on an effect that performs async work'
33
}
34
}
35
*/
36
37
import Effect
Effect
.
const runPromise: <{ readonly id: number; readonly name: string; readonly age: number; }, ParseError>(effect: Effect.Effect<{ readonly id: number; readonly name: string; readonly age: number; }, ParseError, never>, options?: { readonly signal?: AbortSignal; } | undefined) => Promise<...>

Executes an effect and returns a `Promise` that resolves with the result. Use `runPromise` when working with asynchronous effects and you need to integrate with code that uses Promises. If the effect fails, the returned Promise will be rejected with the error.

runPromise
(
import Schema
Schema
.
const decodeUnknown: <{ readonly id: number; readonly name: string; readonly age: number; }, number, never>(schema: Schema.Schema<{ readonly id: number; readonly name: string; readonly age: number; }, number, never>, options?: ParseOptions) => (u: unknown, overrideOptions?: ParseOptions) => Effect.Effect<...>
decodeUnknown
(
const asyncSchema: Schema.transformOrFail<typeof Schema.Number, Schema.Struct<{ id: typeof Schema.Number; name: typeof Schema.String; age: typeof Schema.Number; }>, never>
asyncSchema
)(1)).
(method) Promise<{ readonly id: number; readonly name: string; readonly age: number; }>.then<void, never>(onfulfilled?: ((value: { readonly id: number; readonly name: string; readonly age: number; }) => void | PromiseLike<void>) | null | undefined, onrejected?: ((reason: any) => PromiseLike<...>) | null | undefined): Promise<...>

Attaches callbacks for the resolution and/or rejection of the Promise.

then
(
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
)
38
/*
39
Output:
40
{ id: 1, name: 'name', age: 18 }
41
*/

In the code above, the first approach using Schema.decodeUnknownEither results in an error indicating that the transformation cannot be resolved synchronously. This occurs because Schema.decodeUnknownEither is not designed for async operations. The second approach, which uses Schema.decodeUnknown, works correctly, allowing you to handle asynchronous transformations and return the expected result.

The Schema module provides several encode* functions to encode data according to a schema:

APIDescription
encodeSyncSynchronously encodes data and throws an error if encoding fails.
encodeOptionEncodes data and returns an Option type.
encodeEitherEncodes data and returns an Either type representing success or failure.
encodePromiseEncodes data and returns a Promise.
encodeEncodes data and returns an Effect.

Example (Schema.encodeSync)

1
import {
import Schema
Schema
} from "effect"
2
3
const
const Person: Schema.Struct<{ name: typeof Schema.NonEmptyString; age: typeof Schema.NumberFromString; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.NonEmptyString; age: typeof Schema.NumberFromString; }>(fields: { name: typeof Schema.NonEmptyString; age: typeof Schema.NumberFromString; }): Schema.Struct<{ name: typeof Schema.NonEmptyString; age: typeof Schema.NumberFromString; }> (+1 overload) namespace Struct
Struct
({
4
// A schema that ensures a string is not empty
5
(property) name: typeof Schema.NonEmptyString
name
:
import Schema
Schema
.
class NonEmptyString
NonEmptyString
,
6
// A schema that can decode a string to a number
7
// and encode a number to a string
8
(property) age: typeof Schema.NumberFromString
age
:
import Schema
Schema
.
class NumberFromString

This schema transforms a `string` into a `number` by parsing the string using the `parse` function of the `effect/Number` module. It returns an error if the value can't be converted (for example when non-numeric characters are provided). The following special string values are supported: "NaN", "Infinity", "-Infinity".

NumberFromString
9
})
10
11
// Valid input
12
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
import Schema
Schema
.
(alias) encodeSync<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: string; }>(schema: Schema.Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: string; }, never>, options?: ParseOptions): (a: { readonly name: string; readonly age: number; }, overrideOptions?: ParseOptions) => { readonly name: string; readonly age: string; } export encodeSync
encodeSync
(
const Person: Schema.Struct<{ name: typeof Schema.NonEmptyString; age: typeof Schema.NumberFromString; }>
Person
)({
(property) name: string
name
: "Alice",
(property) age: number
age
: 30 }))
13
// Output: { name: 'Alice', age: '30' }
14
15
// Invalid input
16
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
import Schema
Schema
.
(alias) encodeSync<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: string; }>(schema: Schema.Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: string; }, never>, options?: ParseOptions): (a: { readonly name: string; readonly age: number; }, overrideOptions?: ParseOptions) => { readonly name: string; readonly age: string; } export encodeSync
encodeSync
(
const Person: Schema.Struct<{ name: typeof Schema.NonEmptyString; age: typeof Schema.NumberFromString; }>
Person
)({
(property) name: string
name
: "",
(property) age: number
age
: 30 }))
17
/*
18
throws:
19
ParseError: { readonly name: NonEmptyString; readonly age: NumberFromString }
20
└─ ["name"]
21
└─ NonEmptyString
22
└─ Predicate refinement failure
23
└─ Expected NonEmptyString, actual ""
24
*/

Note that during encoding, the number value 30 was converted to a string "30".

Although it is generally recommended to define schemas that support both decoding and encoding, there are situations where encoding support might be impossible. In such cases, the Forbidden error can be used to handle unsupported encoding.

Example (Using Forbidden for Unsupported Encoding)

Here is an example of a transformation that never fails during decoding. It returns an Either containing either the decoded value or the original input. For encoding, it is reasonable to not support it and use Forbidden as the result.

1
import {
import Either
Either
,
import ParseResult
ParseResult
,
import Schema
Schema
} from "effect"
2
3
// Define a schema that safely decodes to Either type
4
export const
const SafeDecode: <A, I>(self: Schema.Schema<A, I, never>) => Schema.transformOrFail<typeof Schema.Unknown, Schema.EitherFromSelf<Schema.SchemaClass<A, A, never>, typeof Schema.Unknown>, never>
SafeDecode
= <
(type parameter) A in <A, I>(self: Schema.Schema<A, I, never>): Schema.transformOrFail<typeof Schema.Unknown, Schema.EitherFromSelf<Schema.SchemaClass<A, A, never>, typeof Schema.Unknown>, never>
A
,
(type parameter) I in <A, I>(self: Schema.Schema<A, I, never>): Schema.transformOrFail<typeof Schema.Unknown, Schema.EitherFromSelf<Schema.SchemaClass<A, A, never>, typeof Schema.Unknown>, never>
I
>(
(parameter) self: Schema.Schema<A, I, never>
self
:
import Schema
Schema
.
interface Schema<in out A, in out I = A, out R = never> namespace Schema
Schema
<
(type parameter) A in <A, I>(self: Schema.Schema<A, I, never>): Schema.transformOrFail<typeof Schema.Unknown, Schema.EitherFromSelf<Schema.SchemaClass<A, A, never>, typeof Schema.Unknown>, never>
A
,
(type parameter) I in <A, I>(self: Schema.Schema<A, I, never>): Schema.transformOrFail<typeof Schema.Unknown, Schema.EitherFromSelf<Schema.SchemaClass<A, A, never>, typeof Schema.Unknown>, never>
I
, never>) => {
5
const
const decodeUnknownEither: (u: unknown, overrideOptions?: ParseOptions) => Either.Either<A, ParseResult.ParseError>
decodeUnknownEither
=
import Schema
Schema
.
const decodeUnknownEither: <A, I>(schema: Schema.Schema<A, I, never>, options?: ParseOptions) => (u: unknown, overrideOptions?: ParseOptions) => Either.Either<...>
decodeUnknownEither
(
(parameter) self: Schema.Schema<A, I, never>
self
)
6
return
import Schema
Schema
.
const transformOrFail: <Schema.EitherFromSelf<Schema.SchemaClass<A, A, never>, typeof Schema.Unknown>, typeof Schema.Unknown, never, never>(from: typeof Schema.Unknown, to: Schema.EitherFromSelf<...>, options: { ...; } | { ...; }) => Schema.transformOrFail<...> (+1 overload)

Create a new `Schema` by transforming the input and output of an existing `Schema` using the provided decoding functions.

transformOrFail
(
7
import Schema
Schema
.
class Unknown
Unknown
,
8
import Schema
Schema
.
const EitherFromSelf: <Schema.SchemaClass<A, A, never>, typeof Schema.Unknown>({ left, right }: { readonly left: typeof Schema.Unknown; readonly right: Schema.SchemaClass<A, A, never>; }) => Schema.EitherFromSelf<...>
EitherFromSelf
({
9
(property) left: typeof Schema.Unknown
left
:
import Schema
Schema
.
class Unknown
Unknown
,
10
(property) right: Schema.SchemaClass<A, A, never>
right
:
import Schema
Schema
.
const typeSchema: <A, I, never>(schema: Schema.Schema<A, I, never>) => Schema.SchemaClass<A, A, never>

The `typeSchema` function allows you to extract the `Type` portion of a schema, creating a new schema that conforms to the properties defined in the original schema without considering the initial encoding or transformation processes.

typeSchema
(
(parameter) self: Schema.Schema<A, I, never>
self
)
11
}),
12
{
13
(property) strict?: true
strict
: true,
14
(property) decode: (fromA: unknown, options: ParseOptions, ast: Transformation, fromI: unknown) => Effect<Either.Either<A, unknown>, ParseResult.ParseIssue, never>
decode
: (
(parameter) input: unknown
input
) =>
15
import ParseResult
ParseResult
.
const succeed: <Either.Either<A, unknown>>(a: Either.Either<A, unknown>) => Either.Either<Either.Either<A, unknown>, ParseResult.ParseIssue>
succeed
(
16
import Either
Either
.
const mapLeft: <A, ParseResult.ParseError, unknown>(self: Either.Either<A, ParseResult.ParseError>, f: (left: ParseResult.ParseError) => unknown) => Either.Either<...> (+1 overload)

Maps the `Left` side of an `Either` value to a new `Either` value.

mapLeft
(
const decodeUnknownEither: (u: unknown, overrideOptions?: ParseOptions) => Either.Either<A, ParseResult.ParseError>
decodeUnknownEither
(
(parameter) input: unknown
input
), () =>
(parameter) input: unknown
input
)
17
),
18
(property) encode: (toI: Either.Either<A, unknown>, options: ParseOptions, ast: Transformation, toA: Either.Either<A, unknown>) => Effect<...>
encode
: (
(parameter) actual: Either.Either<A, unknown>
actual
,
(parameter) _: ParseOptions
_
,
(parameter) ast: Transformation
ast
) =>
19
import Either
Either
.
const match: <A, unknown, Either.Either<never, ParseResult.ParseIssue>, Either.Either<A, ParseResult.ParseIssue>>(self: Either.Either<A, unknown>, options: { ...; }) => Either.Either<...> | Either.Either<...> (+1 overload)

Takes two functions and an `Either` value, if the value is a `Left` the inner value is applied to the `onLeft function, if the value is a `Right` the inner value is applied to the `onRight` function.

match
(
(parameter) actual: Either.Either<A, unknown>
actual
, {
20
// Encoding a Left value is not supported
21
(property) onLeft: (left: unknown) => Either.Either<never, ParseResult.ParseIssue>
onLeft
: () =>
22
import ParseResult
ParseResult
.
const fail: (issue: ParseResult.ParseIssue) => Either.Either<never, ParseResult.ParseIssue>
fail
(
23
new
import ParseResult
ParseResult
.
constructor Forbidden(ast: AST, actual: unknown, message?: string | undefined): ParseResult.Forbidden

The `Forbidden` variant of the `ParseIssue` type represents a forbidden operation, such as when encountering an Effect that is not allowed to execute (e.g., using `runSync`).

Forbidden
(
24
(parameter) ast: Transformation
ast
,
25
(parameter) actual: Either.Either<A, unknown>
actual
,
26
"cannot encode a Left"
27
)
28
),
29
// Successfully encode a Right value
30
(property) onRight: (right: A) => Either.Either<A, ParseResult.ParseIssue>
onRight
:
import ParseResult
ParseResult
.
const succeed: <A>(a: A) => Either.Either<A, ParseResult.ParseIssue>
succeed
31
})
32
}
33
)
34
}

Explanation

  • Decoding: The SafeDecode function ensures that decoding never fails. It wraps the decoded value in an Either, where a successful decoding results in a Right and a failed decoding results in a Left containing the original input.
  • Encoding: The encoding process uses the Forbidden error to indicate that encoding a Left value is not supported. Only Right values are successfully encoded.

The Schema.decodeUnknownEither and Schema.encodeEither functions returns a Either:

Either<Type, ParseError>

where ParseError is defined as follows (simplified):

interface ParseError {
readonly _tag: "ParseError"
readonly issue: ParseIssue
}

In this structure, ParseIssue represents an error that might occur during the parsing process. It is wrapped in a tagged error to make it easier to catch errors using Effect.catchTag. The result Either<Type, ParseError> contains the inferred data type described by the schema (Type). A successful parse yields a Right value with the parsed data Type, while a failed parse results in a Left value containing a ParseError.

The following options affect both decoding and encoding.

When using a schema to parse a value, by default any properties that are not specified in the schema will be stripped out from the output. This is because the schema is expecting a specific shape for the parsed value, and any excess properties do not conform to that shape.

However, you can use the onExcessProperty option (default value: "ignore") to trigger a parsing error. This can be particularly useful in cases where you need to detect and handle potential errors or unexpected values.

Example (onExcessProperty set to "error")

1
import {
import Schema
Schema
} from "effect"
2
3
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
6
})
7
8
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
9
import Schema
Schema
.
(alias) decodeUnknownSync<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }>(schema: Schema.Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>, options?: ParseOptions): (u: unknown, overrideOptions?: ParseOptions) => { readonly name: string; readonly age: number; } export decodeUnknownSync
decodeUnknownSync
(
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
)({
10
(property) name: string
name
: "Bob",
11
(property) age: number
age
: 40,
12
(property) email: string
email
: "[email protected]"
13
})
14
)
15
/*
16
Output:
17
{ name: 'Bob', age: 40 }
18
*/
19
20
import Schema
Schema
.
(alias) decodeUnknownSync<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }>(schema: Schema.Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>, options?: ParseOptions): (u: unknown, overrideOptions?: ParseOptions) => { readonly name: string; readonly age: number; } export decodeUnknownSync
decodeUnknownSync
(
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
)(
21
{
22
(property) name: string
name
: "Bob",
23
(property) age: number
age
: 40,
24
(property) email: string
email
: "[email protected]"
25
},
26
{
(property) ParseOptions.onExcessProperty?: "ignore" | "error" | "preserve" | undefined

When using a `Schema` to parse a value, by default any properties that are not specified in the `Schema` will be stripped out from the output. This is because the `Schema` is expecting a specific shape for the parsed value, and any excess properties do not conform to that shape. However, you can use the `onExcessProperty` option (default value: `"ignore"`) to trigger a parsing error. This can be particularly useful in cases where you need to detect and handle potential errors or unexpected values. If you want to allow excess properties to remain, you can use `onExcessProperty` set to `"preserve"`. default: "ignore"

onExcessProperty
: "error" }
27
)
28
/*
29
throws
30
ParseError: { readonly name: string; readonly age: number }
31
└─ ["email"]
32
└─ is unexpected, expected: "name" | "age"
33
*/

If you want to allow excess properties to remain, you can use onExcessProperty set to "preserve".

Example (onExcessProperty set to "preserve")

1
import {
import Schema
Schema
} from "effect"
2
3
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
6
})
7
8
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
9
import Schema
Schema
.
(alias) decodeUnknownSync<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }>(schema: Schema.Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>, options?: ParseOptions): (u: unknown, overrideOptions?: ParseOptions) => { readonly name: string; readonly age: number; } export decodeUnknownSync
decodeUnknownSync
(
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
)(
10
{
11
(property) name: string
name
: "Bob",
12
(property) age: number
age
: 40,
13
(property) email: string
email
: "[email protected]"
14
},
15
{
(property) ParseOptions.onExcessProperty?: "ignore" | "error" | "preserve" | undefined

When using a `Schema` to parse a value, by default any properties that are not specified in the `Schema` will be stripped out from the output. This is because the `Schema` is expecting a specific shape for the parsed value, and any excess properties do not conform to that shape. However, you can use the `onExcessProperty` option (default value: `"ignore"`) to trigger a parsing error. This can be particularly useful in cases where you need to detect and handle potential errors or unexpected values. If you want to allow excess properties to remain, you can use `onExcessProperty` set to `"preserve"`. default: "ignore"

onExcessProperty
: "preserve" }
16
)
17
)
18
/*
19
{ email: '[email protected]', name: 'Bob', age: 40 }
20
*/

The errors option allows you to receive all parsing errors when attempting to parse a value using a schema. By default only the first error is returned, but by setting the errors option to "all", you can receive all errors that occurred during the parsing process. This can be useful for debugging or for providing more comprehensive error messages to the user.

Example (errors set to "all")

1
import {
import Schema
Schema
} from "effect"
2
3
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
4
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
5
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
6
})
7
8
import Schema
Schema
.
(alias) decodeUnknownSync<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }>(schema: Schema.Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>, options?: ParseOptions): (u: unknown, overrideOptions?: ParseOptions) => { readonly name: string; readonly age: number; } export decodeUnknownSync
decodeUnknownSync
(
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
)(
9
{
10
(property) name: string
name
: "Bob",
11
(property) age: string
age
: "abc",
12
(property) email: string
email
: "[email protected]"
13
},
14
{
(property) ParseOptions.errors?: "first" | "all" | undefined

The `errors` option allows you to receive all parsing errors when attempting to parse a value using a schema. By default only the first error is returned, but by setting the `errors` option to `"all"`, you can receive all errors that occurred during the parsing process. This can be useful for debugging or for providing more comprehensive error messages to the user. default: "first"

errors
: "all",
(property) ParseOptions.onExcessProperty?: "ignore" | "error" | "preserve" | undefined

When using a `Schema` to parse a value, by default any properties that are not specified in the `Schema` will be stripped out from the output. This is because the `Schema` is expecting a specific shape for the parsed value, and any excess properties do not conform to that shape. However, you can use the `onExcessProperty` option (default value: `"ignore"`) to trigger a parsing error. This can be particularly useful in cases where you need to detect and handle potential errors or unexpected values. If you want to allow excess properties to remain, you can use `onExcessProperty` set to `"preserve"`. default: "ignore"

onExcessProperty
: "error" }
15
)
16
/*
17
throws
18
ParseError: { readonly name: string; readonly age: number }
19
├─ ["email"]
20
│ └─ is unexpected, expected: "name" | "age"
21
└─ ["age"]
22
└─ Expected number, actual "abc"
23
*/

The propertyOrder option provides control over the order of object fields in the output. This feature is particularly useful when the sequence of keys is important for the consuming processes or when maintaining the input order enhances readability and usability.

By default, the propertyOrder option is set to "none". This means that the internal system decides the order of keys to optimize parsing speed. The order of keys in this mode should not be considered stable, and it’s recommended not to rely on key ordering as it may change in future updates.

Setting propertyOrder to "original" ensures that the keys are ordered as they appear in the input during the decoding/encoding process.

Example (Synchronous Decoding)

1
import {
import Schema
Schema
} from "effect"
2
3
const
const schema: Schema.Struct<{ a: typeof Schema.Number; b: Schema.Literal<["b"]>; c: typeof Schema.Number; }>
schema
=
import Schema
Schema
.
function Struct<{ a: typeof Schema.Number; b: Schema.Literal<["b"]>; c: typeof Schema.Number; }>(fields: { a: typeof Schema.Number; b: Schema.Literal<["b"]>; c: typeof Schema.Number; }): Schema.Struct<...> (+1 overload) namespace Struct
Struct
({
4
(property) a: typeof Schema.Number
a
:
import Schema
Schema
.
(alias) class Number export Number
Number
,
5
(property) b: Schema.Literal<["b"]>
b
:
import Schema
Schema
.
function Literal<["b"]>(literals_0: "b"): Schema.Literal<["b"]> (+2 overloads)
Literal
("b"),
6
(property) c: typeof Schema.Number
c
:
import Schema
Schema
.
(alias) class Number export Number
Number
7
})
8
9
// Decoding an object synchronously without specifying the property order
10
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
import Schema
Schema
.
(alias) decodeUnknownSync<{ readonly a: number; readonly b: "b"; readonly c: number; }, { readonly a: number; readonly b: "b"; readonly c: number; }>(schema: Schema.Schema<{ readonly a: number; readonly b: "b"; readonly c: number; }, { readonly a: number; readonly b: "b"; readonly c: number; }, never>, options?: ParseOptions): (u: unknown, overrideOptions?: ParseOptions) => { readonly a: number; readonly b: "b"; readonly c: number; } export decodeUnknownSync
decodeUnknownSync
(
const schema: Schema.Struct<{ a: typeof Schema.Number; b: Schema.Literal<["b"]>; c: typeof Schema.Number; }>
schema
)({
(property) b: string
b
: "b",
(property) c: number
c
: 2,
(property) a: number
a
: 1 }))
11
// Output decided internally: { a: 1, b: 'b', c: 2 }
12
13
// Decoding an object synchronously while preserving the order of properties as in the input
14
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
15
import Schema
Schema
.
(alias) decodeUnknownSync<{ readonly a: number; readonly b: "b"; readonly c: number; }, { readonly a: number; readonly b: "b"; readonly c: number; }>(schema: Schema.Schema<{ readonly a: number; readonly b: "b"; readonly c: number; }, { readonly a: number; readonly b: "b"; readonly c: number; }, never>, options?: ParseOptions): (u: unknown, overrideOptions?: ParseOptions) => { readonly a: number; readonly b: "b"; readonly c: number; } export decodeUnknownSync
decodeUnknownSync
(
const schema: Schema.Struct<{ a: typeof Schema.Number; b: Schema.Literal<["b"]>; c: typeof Schema.Number; }>
schema
)(
16
{
(property) b: string
b
: "b",
(property) c: number
c
: 2,
(property) a: number
a
: 1 },
17
{
(property) ParseOptions.propertyOrder?: "none" | "original" | undefined

The `propertyOrder` option provides control over the order of object fields in the output. This feature is particularly useful when the sequence of keys is important for the consuming processes or when maintaining the input order enhances readability and usability. By default, the `propertyOrder` option is set to `"none"`. This means that the internal system decides the order of keys to optimize parsing speed. The order of keys in this mode should not be considered stable, and it's recommended not to rely on key ordering as it may change in future updates without notice. Setting `propertyOrder` to `"original"` ensures that the keys are ordered as they appear in the input during the decoding/encoding process. default: "none"

propertyOrder
: "original" }
18
)
19
)
20
// Output preserving input order: { b: 'b', c: 2, a: 1 }

Example (Asynchronous Decoding)

1
import type {
import Duration
Duration
} from "effect"
2
import {
import Effect
Effect
,
import ParseResult
ParseResult
,
import Schema
Schema
} from "effect"
3
4
// Function to simulate an asynchronous process within the schema
5
const
const effectify: (duration: Duration.DurationInput) => Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>
effectify
= (
(parameter) duration: Duration.DurationInput
duration
:
import Duration
Duration
.
type DurationInput = number | bigint | Duration.Duration | [seconds: number, nanos: number] | `${number} nano` | `${number} nanos` | `${number} micro` | `${number} micros` | `${number} milli` | `${number} millis` | `${number} second` | `${number} seconds` | `${number} minute` | `${number} minutes` | ... 5 more ... | `${number} weeks`
DurationInput
) =>
6
import Schema
Schema
.
(alias) class Number export Number
Number
.
(method) Pipeable.pipe<typeof Schema.Number, Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>>(this: typeof Schema.Number, ab: (_: typeof Schema.Number) => Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>): Schema.transformOrFail<...> (+21 overloads)
pipe
(
7
import Schema
Schema
.
const transformOrFail: <typeof Schema.Number, typeof Schema.Number, never, never>(to: typeof Schema.Number, options: { readonly decode: (fromA: number, options: ParseOptions, ast: Transformation, fromI: number) => Effect.Effect<...>; readonly encode: (toI: number, options: ParseOptions, ast: Transformation, toA: number) => Effect.Effect<...>; readonly strict?: true; } | { ...; }) => (from: typeof Schema.Number) => Schema.transformOrFail<...> (+1 overload)

Create a new `Schema` by transforming the input and output of an existing `Schema` using the provided decoding functions.

transformOrFail
(
import Schema
Schema
.
(alias) class Number export Number
Number
, {
8
(property) strict?: true
strict
: true,
9
(property) decode: (fromA: number, options: ParseOptions, ast: Transformation, fromI: number) => Effect.Effect<number, ParseResult.ParseIssue, never>
decode
: (
(parameter) x: number
x
) =>
10
import Effect
Effect
.
const sleep: (duration: Duration.DurationInput) => Effect.Effect<void>

Returns an effect that suspends for the specified duration. This method is asynchronous, and does not actually block the fiber executing the effect.

sleep
(
(parameter) duration: Duration.DurationInput
duration
).
(method) Pipeable.pipe<Effect.Effect<void, never, never>, Effect.Effect<number, ParseResult.ParseIssue, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, never, never>) => Effect.Effect<...>): Effect.Effect<...> (+21 overloads)
pipe
(
11
import Effect
Effect
.
const andThen: <Either<number, ParseResult.ParseIssue>>(f: Either<number, ParseResult.ParseIssue>) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<...> (+3 overloads)

Executes a sequence of two actions, typically two `Effect`s, where the second action can depend on the result of the first action. The `that` action can take various forms: - a value - a function returning a value - a promise - a function returning a promise - an effect - a function returning an effect

andThen
(
import ParseResult
ParseResult
.
const succeed: <number>(a: number) => Either<number, ParseResult.ParseIssue>
succeed
(
(parameter) x: number
x
))
12
),
13
(property) encode: (toI: number, options: ParseOptions, ast: Transformation, toA: number) => Effect.Effect<number, ParseResult.ParseIssue, never>
encode
:
import ParseResult
ParseResult
.
const succeed: <A>(a: A) => Either<A, ParseResult.ParseIssue>
succeed
14
})
15
)
16
17
// Define a structure with asynchronous behavior in each field
18
const
const schema: Schema.Struct<{ a: Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>; b: Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>; c: Schema.transformOrFail<...>; }>
schema
=
import Schema
Schema
.
function Struct<{ a: Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>; b: Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>; c: Schema.transformOrFail<...>; }>(fields: { ...; }): Schema.Struct<...> (+1 overload) namespace Struct
Struct
({
19
(property) a: Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>
a
:
const effectify: (duration: Duration.DurationInput) => Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>
effectify
("200 millis"),
20
(property) b: Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>
b
:
const effectify: (duration: Duration.DurationInput) => Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>
effectify
("300 millis"),
21
(property) c: Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>
c
:
const effectify: (duration: Duration.DurationInput) => Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>
effectify
("100 millis")
22
}).
(method) Struct<{ a: transformOrFail<typeof Number$, typeof Number$, never>; b: transformOrFail<typeof Number$, typeof Number$, never>; c: transformOrFail<typeof Number$, typeof Number$, never>; }>.annotations(annotations: Schema.Annotations.Schema<{ readonly a: number; readonly b: number; readonly c: number; }, readonly []>): Schema.Struct<{ a: Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>; b: Schema.transformOrFail<...>; c: Schema.transformOrFail<...>; }>

Merges a set of new annotations with existing ones, potentially overwriting any duplicates.

annotations
({
(property) Annotations.Schema<{ readonly a: number; readonly b: number; readonly c: number; }, readonly []>.concurrency?: ConcurrencyAnnotation
concurrency
: 3 })
23
24
// Decoding data asynchronously without preserving order
25
import Schema
Schema
.
const decode: <{ readonly a: number; readonly b: number; readonly c: number; }, { readonly a: number; readonly b: number; readonly c: number; }, never>(schema: Schema.Schema<{ readonly a: number; readonly b: number; readonly c: number; }, { ...; }, never>, options?: ParseOptions) => (i: { ...; }, overrideOptions?: ParseOptions) => Effect.Effect<...>
decode
(
const schema: Schema.Struct<{ a: Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>; b: Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>; c: Schema.transformOrFail<...>; }>
schema
)({
(property) a: number
a
: 1,
(property) b: number
b
: 2,
(property) c: number
c
: 3 })
26
.
(method) Pipeable.pipe<Effect.Effect<{ readonly a: number; readonly b: number; readonly c: number; }, ParseResult.ParseError, never>, Promise<{ readonly a: number; readonly b: number; readonly c: number; }>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<...>) => Promise<...>): Promise<...> (+21 overloads)
pipe
(
import Effect
Effect
.
const runPromise: <A, E>(effect: Effect.Effect<A, E, never>, options?: { readonly signal?: AbortSignal; } | undefined) => Promise<A>

Executes an effect and returns a `Promise` that resolves with the result. Use `runPromise` when working with asynchronous effects and you need to integrate with code that uses Promises. If the effect fails, the returned Promise will be rejected with the error.

runPromise
)
27
.
(method) Promise<{ readonly a: number; readonly b: number; readonly c: number; }>.then<void, never>(onfulfilled?: ((value: { readonly a: number; readonly b: number; readonly c: number; }) => void | PromiseLike<void>) | null | undefined, onrejected?: ((reason: any) => PromiseLike<...>) | null | undefined): Promise<...>

Attaches callbacks for the resolution and/or rejection of the Promise.

then
(
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
)
28
// Output decided internally: { c: 3, a: 1, b: 2 }
29
30
// Decoding data asynchronously while preserving the original input order
31
import Schema
Schema
.
const decode: <{ readonly a: number; readonly b: number; readonly c: number; }, { readonly a: number; readonly b: number; readonly c: number; }, never>(schema: Schema.Schema<{ readonly a: number; readonly b: number; readonly c: number; }, { ...; }, never>, options?: ParseOptions) => (i: { ...; }, overrideOptions?: ParseOptions) => Effect.Effect<...>
decode
(
const schema: Schema.Struct<{ a: Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>; b: Schema.transformOrFail<typeof Schema.Number, typeof Schema.Number, never>; c: Schema.transformOrFail<...>; }>
schema
)({
(property) a: number
a
: 1,
(property) b: number
b
: 2,
(property) c: number
c
: 3 }, {
(property) ParseOptions.propertyOrder?: "none" | "original" | undefined

The `propertyOrder` option provides control over the order of object fields in the output. This feature is particularly useful when the sequence of keys is important for the consuming processes or when maintaining the input order enhances readability and usability. By default, the `propertyOrder` option is set to `"none"`. This means that the internal system decides the order of keys to optimize parsing speed. The order of keys in this mode should not be considered stable, and it's recommended not to rely on key ordering as it may change in future updates without notice. Setting `propertyOrder` to `"original"` ensures that the keys are ordered as they appear in the input during the decoding/encoding process. default: "none"

propertyOrder
: "original" })
32
.
(method) Pipeable.pipe<Effect.Effect<{ readonly a: number; readonly b: number; readonly c: number; }, ParseResult.ParseError, never>, Promise<{ readonly a: number; readonly b: number; readonly c: number; }>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<...>) => Promise<...>): Promise<...> (+21 overloads)
pipe
(
import Effect
Effect
.
const runPromise: <A, E>(effect: Effect.Effect<A, E, never>, options?: { readonly signal?: AbortSignal; } | undefined) => Promise<A>

Executes an effect and returns a `Promise` that resolves with the result. Use `runPromise` when working with asynchronous effects and you need to integrate with code that uses Promises. If the effect fails, the returned Promise will be rejected with the error.

runPromise
)
33
.
(method) Promise<{ readonly a: number; readonly b: number; readonly c: number; }>.then<void, never>(onfulfilled?: ((value: { readonly a: number; readonly b: number; readonly c: number; }) => void | PromiseLike<void>) | null | undefined, onrejected?: ((reason: any) => PromiseLike<...>) | null | undefined): Promise<...>

Attaches callbacks for the resolution and/or rejection of the Promise.

then
(
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
)
34
// Output preserving input order: { a: 1, b: 2, c: 3 }

You can tailor parse options for each schema using the parseOptions annotation. These options allow for specific parsing behavior at various levels of the schema hierarchy, overriding any parent settings and cascading down to nested schemas.

Example

1
import {
import Schema
Schema
} from "effect"
2
import {
import Either
Either
} from "effect"
3
4
const
const schema: Schema.Struct<{ a: Schema.Struct<{ b: typeof Schema.String; c: typeof Schema.String; }>; d: typeof Schema.String; }>
schema
=
import Schema
Schema
.
function Struct<{ a: Schema.Struct<{ b: typeof Schema.String; c: typeof Schema.String; }>; d: typeof Schema.String; }>(fields: { a: Schema.Struct<{ b: typeof Schema.String; c: typeof Schema.String; }>; d: typeof Schema.String; }): Schema.Struct<...> (+1 overload) namespace Struct
Struct
({
5
(property) a: Schema.Struct<{ b: typeof Schema.String; c: typeof Schema.String; }>
a
:
import Schema
Schema
.
function Struct<{ b: typeof Schema.String; c: typeof Schema.String; }>(fields: { b: typeof Schema.String; c: typeof Schema.String; }): Schema.Struct<{ b: typeof Schema.String; c: typeof Schema.String; }> (+1 overload) namespace Struct
Struct
({
6
(property) b: typeof Schema.String
b
:
import Schema
Schema
.
(alias) class String export String
String
,
7
(property) c: typeof Schema.String
c
:
import Schema
Schema
.
(alias) class String export String
String
8
}).
(method) Struct<{ b: typeof String$; c: typeof String$; }>.annotations(annotations: Schema.Annotations.Schema<{ readonly b: string; readonly c: string; }, readonly []>): Schema.Struct<{ b: typeof Schema.String; c: typeof Schema.String; }>

Merges a set of new annotations with existing ones, potentially overwriting any duplicates.

annotations
({
9
(property) Annotations.Doc<{ readonly b: string; readonly c: string; }>.title?: string
title
: "first error only",
10
// Only the first error in this sub-schema is reported
11
(property) Annotations.Schema<{ readonly b: string; readonly c: string; }, readonly []>.parseOptions?: ParseOptions
parseOptions
: {
(property) ParseOptions.errors?: "first" | "all" | undefined

The `errors` option allows you to receive all parsing errors when attempting to parse a value using a schema. By default only the first error is returned, but by setting the `errors` option to `"all"`, you can receive all errors that occurred during the parsing process. This can be useful for debugging or for providing more comprehensive error messages to the user. default: "first"

errors
: "first" }
12
}),
13
(property) d: typeof Schema.String
d
:
import Schema
Schema
.
(alias) class String export String
String
14
}).
(method) Struct<{ a: Struct<{ b: typeof String$; c: typeof String$; }>; d: typeof String$; }>.annotations(annotations: Schema.Annotations.Schema<{ readonly a: { readonly b: string; readonly c: string; }; readonly d: string; }, readonly []>): Schema.Struct<{ a: Schema.Struct<{ b: typeof Schema.String; c: typeof Schema.String; }>; d: typeof Schema.String; }>

Merges a set of new annotations with existing ones, potentially overwriting any duplicates.

annotations
({
15
(property) Annotations.Doc<A>.title?: string
title
: "all errors",
16
// All errors in the main schema are reported
17
(property) Annotations.Schema<A, TypeParameters extends ReadonlyArray<any> = readonly []>.parseOptions?: ParseOptions
parseOptions
: {
(property) ParseOptions.errors?: "first" | "all" | undefined

The `errors` option allows you to receive all parsing errors when attempting to parse a value using a schema. By default only the first error is returned, but by setting the `errors` option to `"all"`, you can receive all errors that occurred during the parsing process. This can be useful for debugging or for providing more comprehensive error messages to the user. default: "first"

errors
: "all" }
18
})
19
20
const
const result: Either.Either<{ readonly a: { readonly b: string; readonly c: string; }; readonly d: string; }, ParseError>
result
=
import Schema
Schema
.
const decodeUnknownEither: <{ readonly a: { readonly b: string; readonly c: string; }; readonly d: string; }, { readonly a: { readonly b: string; readonly c: string; }; readonly d: string; }>(schema: Schema.Schema<{ readonly a: { readonly b: string; readonly c: string; }; readonly d: string; }, { ...; }, never>, options?: ParseOptions) => (u: unknown, overrideOptions?: ParseOptions) => Either.Either<...>
decodeUnknownEither
(
const schema: Schema.Struct<{ a: Schema.Struct<{ b: typeof Schema.String; c: typeof Schema.String; }>; d: typeof Schema.String; }>
schema
)(
21
{
(property) a: {}
a
: {} },
22
{
(property) ParseOptions.errors?: "first" | "all" | undefined

The `errors` option allows you to receive all parsing errors when attempting to parse a value using a schema. By default only the first error is returned, but by setting the `errors` option to `"all"`, you can receive all errors that occurred during the parsing process. This can be useful for debugging or for providing more comprehensive error messages to the user. default: "first"

errors
: "first" }
23
)
24
if (
import Either
Either
.
const isLeft: <{ readonly a: { readonly b: string; readonly c: string; }; readonly d: string; }, ParseError>(self: Either.Either<{ readonly a: { readonly b: string; readonly c: string; }; readonly d: string; }, ParseError>) => self is Either.Left<...>

Determine if a `Either` is a `Left`.

isLeft
(
const result: Either.Either<{ readonly a: { readonly b: string; readonly c: string; }; readonly d: string; }, ParseError>
result
)) {
25
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
const result: Either.Left<ParseError, { readonly a: { readonly b: string; readonly c: string; }; readonly d: string; }>
result
.
(property) Left<ParseError, { readonly a: { readonly b: string; readonly c: string; }; readonly d: string; }>.left: ParseError
left
.
(property) ParseError.message: string
message
)
26
}
27
/*
28
all errors
29
├─ ["a"]
30
│ └─ first error only
31
│ └─ ["b"]
32
│ └─ is missing
33
└─ ["d"]
34
└─ is missing
35
*/

Detailed Output Explanation:

In this example:

  • The main schema is configured to display all errors. Hence, you will see errors related to both the d field (since it’s missing) and any errors from the a subschema.
  • The subschema (a) is set to display only the first error. Although both b and c fields are missing, only the first missing field (b) is reported.

The Schema.is function provides a way to verify if a value conforms to a given schema. It acts as a type guard, taking a value of type unknown and determining if it matches the structure and type constraints defined in the schema.

Here’s how the Schema.is function works:

  1. Schema Definition: Define a schema to describe the structure and constraints of the data type you expect. For instance, Schema<Type, Encoded, Context>, where Type is the target type you want to validate against.

  2. Type Guard Creation: Use the schema to create a user-defined type guard, (u: unknown) => u is Type. This function can be used at runtime to check if a value meets the requirements of the schema.

Example (Creating and Using a Type Guard)

1
import {
import Schema
Schema
} from "effect"
2
3
// Define a schema for a Person object
4
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
5
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
6
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
7
})
8
9
// Create a type guard using the schema
10
const
const isPerson: (u: unknown, overrideOptions?: ParseOptions | number) => u is { readonly name: string; readonly age: number; }
isPerson
=
import Schema
Schema
.
(alias) is<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>(schema: Schema.Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>, options?: ParseOptions): (u: unknown, overrideOptions?: ParseOptions | number) => u is { readonly name: string; readonly age: number; } export is

By default the option `exact` is set to `true`.

is
(
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
)
11
12
// Test the type guard with different values
13
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
const isPerson: (u: unknown, overrideOptions?: ParseOptions | number) => u is { readonly name: string; readonly age: number; }
isPerson
({
(property) name: string
name
: "Alice",
(property) age: number
age
: 30 })) // true
14
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
const isPerson: (u: unknown, overrideOptions?: ParseOptions | number) => u is { readonly name: string; readonly age: number; }
isPerson
(null)) // false
15
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
const isPerson: (u: unknown, overrideOptions?: ParseOptions | number) => u is { readonly name: string; readonly age: number; }
isPerson
({})) // false

The isPerson function generated from the schema has the following signature:

const isPerson: (
u: unknown,
overrideOptions?: number | ParseOptions
) => u is {
readonly name: string
readonly age: number
}

While type guards verify whether a value conforms to a specific type, the Schema.asserts function goes further by asserting that an input matches the schema type Type (from Schema<Type, Encoded, Context>). If the input does not match the schema, it throws a detailed error, making it useful for runtime validation.

Example (Creating and Using an Assertion)

1
import {
import Schema
Schema
} from "effect"
2
3
// Define a schema for a Person object
4
const
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
=
import Schema
Schema
.
function Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>(fields: { name: typeof Schema.String; age: typeof Schema.Number; }): Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }> (+1 overload) namespace Struct
Struct
({
5
(property) name: typeof Schema.String
name
:
import Schema
Schema
.
(alias) class String export String
String
,
6
(property) age: typeof Schema.Number
age
:
import Schema
Schema
.
(alias) class Number export Number
Number
7
})
8
9
// Create an assertion function from the schema
10
const
const assertsPerson: Schema.Schema.ToAsserts<Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>>
assertsPerson
:
import Schema
Schema
.
namespace Schema
Schema
.
type Schema<in out A, in out I = A, out R = never>.ToAsserts<S extends Schema.Schema.AnyNoContext> = (input: unknown, options?: ParseOptions) => asserts input is Schema.Schema.Type<S>
ToAsserts
<typeof
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
> =
11
import Schema
Schema
.
(alias) asserts<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>(schema: Schema.Schema<{ readonly name: string; readonly age: number; }, { readonly name: string; readonly age: number; }, never>, options?: ParseOptions): (u: unknown, overrideOptions?: ParseOptions) => asserts u is { readonly name: string; readonly age: number; } export asserts

By default the option `exact` is set to `true`.

asserts
(
const Person: Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>
Person
)
12
13
try {
14
// Attempt to assert that the input matches the Person schema
15
const assertsPerson: (input: unknown, options?: ParseOptions) => asserts input is Schema.Schema<in out A, in out I = A, out R = never>.Type<Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>>
assertsPerson
({
(property) name: string
name
: "Alice",
(property) age: string
age
: "30" })
16
} catch (
var e: unknown
e
) {
17
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.error(message?: any, ...optionalParams: any[]): void

Prints to `stderr` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const code = 5; console.error('error #%d', code); // Prints: error #5, to stderr console.error('error', code); // Prints: error 5, to stderr ``` If formatting elements (e.g. `%d`) are not found in the first string then [`util.inspect()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilinspectobject-options) is called on each argument and the resulting string values are concatenated. See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

error
("The input does not match the schema:")
18
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.error(message?: any, ...optionalParams: any[]): void

Prints to `stderr` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const code = 5; console.error('error #%d', code); // Prints: error #5, to stderr console.error('error', code); // Prints: error 5, to stderr ``` If formatting elements (e.g. `%d`) are not found in the first string then [`util.inspect()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilinspectobject-options) is called on each argument and the resulting string values are concatenated. See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

error
(
var e: unknown
e
)
19
}
20
/*
21
throws:
22
The input does not match the schema:
23
{
24
_id: 'ParseError',
25
message: '{ readonly name: string; readonly age: number }\n' +
26
'└─ ["age"]\n' +
27
' └─ Expected number, actual "30"'
28
}
29
*/
30
31
// This input matches the schema and will not throw an error
32
const assertsPerson: (input: unknown, options?: ParseOptions) => asserts input is Schema.Schema<in out A, in out I = A, out R = never>.Type<Schema.Struct<{ name: typeof Schema.String; age: typeof Schema.Number; }>>
assertsPerson
({
(property) name: string
name
: "Alice",
(property) age: number
age
: 30 })

The assertsPerson function generated from the schema has the following signature:

const assertsPerson: (
input: unknown,
overrideOptions?: number | ParseOptions
) => asserts input is {
readonly name: string
readonly age: number
}

When decoding, it’s important to understand how missing properties are processed. By default, if a property is not present in the input, it is treated as if it were present with an undefined value.

Example (Default Behavior)

1
import {
import Schema
Schema
} from "effect"
2
3
const
const schema: Schema.Struct<{ a: typeof Schema.Unknown; }>
schema
=
import Schema
Schema
.
function Struct<{ a: typeof Schema.Unknown; }>(fields: { a: typeof Schema.Unknown; }): Schema.Struct<{ a: typeof Schema.Unknown; }> (+1 overload) namespace Struct
Struct
({
(property) a: typeof Schema.Unknown
a
:
import Schema
Schema
.
class Unknown
Unknown
})
4
const
const input: {}
input
= {}
5
6
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
import Schema
Schema
.
(alias) decodeUnknownSync<{ readonly a: unknown; }, { readonly a: unknown; }>(schema: Schema.Schema<{ readonly a: unknown; }, { readonly a: unknown; }, never>, options?: ParseOptions): (u: unknown, overrideOptions?: ParseOptions) => { readonly a: unknown; } export decodeUnknownSync
decodeUnknownSync
(
const schema: Schema.Struct<{ a: typeof Schema.Unknown; }>
schema
)(
const input: {}
input
))
7
// Output: { a: undefined }

In this example, although the key "a" is not present in the input, it is treated as { a: undefined } by default.

If your validation logic needs to distinguish between truly missing properties and those that are explicitly undefined, you can enable the exact option:

Example (exact set to true)

1
import {
import Schema
Schema
} from "effect"
2
3
const
const schema: Schema.Struct<{ a: typeof Schema.Unknown; }>
schema
=
import Schema
Schema
.
function Struct<{ a: typeof Schema.Unknown; }>(fields: { a: typeof Schema.Unknown; }): Schema.Struct<{ a: typeof Schema.Unknown; }> (+1 overload) namespace Struct
Struct
({
(property) a: typeof Schema.Unknown
a
:
import Schema
Schema
.
class Unknown
Unknown
})
4
const
const input: {}
input
= {}
5
6
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
import Schema
Schema
.
(alias) decodeUnknownSync<{ readonly a: unknown; }, { readonly a: unknown; }>(schema: Schema.Schema<{ readonly a: unknown; }, { readonly a: unknown; }, never>, options?: ParseOptions): (u: unknown, overrideOptions?: ParseOptions) => { readonly a: unknown; } export decodeUnknownSync
decodeUnknownSync
(
const schema: Schema.Struct<{ a: typeof Schema.Unknown; }>
schema
)(
const input: {}
input
, {
(property) ParseOptions.exact?: boolean | undefined

Handles missing properties in data structures. By default, missing properties are treated as if present with an `undefined` value. To treat missing properties as errors, set the `exact` option to `true`. This setting is already enabled by default for `is` and `asserts` functions, treating absent properties strictly unless overridden. default: false

exact
: true }))
7
/*
8
throws
9
ParseError: { readonly a: unknown }
10
└─ ["a"]
11
└─ is missing
12
*/

For the APIs Schema.is and Schema.asserts, however, the default behavior is to treat missing properties strictly, where the default for exact is true:

Example (Default Behavior for Schema.is and Schema.asserts)

1
import type {
import SchemaAST
SchemaAST
} from "effect"
2
import {
import Schema
Schema
} from "effect"
3
4
const
const schema: Schema.Struct<{ a: typeof Schema.Unknown; }>
schema
=
import Schema
Schema
.
function Struct<{ a: typeof Schema.Unknown; }>(fields: { a: typeof Schema.Unknown; }): Schema.Struct<{ a: typeof Schema.Unknown; }> (+1 overload) namespace Struct
Struct
({
(property) a: typeof Schema.Unknown
a
:
import Schema
Schema
.
class Unknown
Unknown
})
5
const
const input: {}
input
= {}
6
7
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
import Schema
Schema
.
(alias) is<{ readonly a: unknown; }, { readonly a: unknown; }, never>(schema: Schema.Schema<{ readonly a: unknown; }, { readonly a: unknown; }, never>, options?: SchemaAST.ParseOptions): (u: unknown, overrideOptions?: SchemaAST.ParseOptions | number) => u is { readonly a: unknown; } export is

By default the option `exact` is set to `true`.

is
(
const schema: Schema.Struct<{ a: typeof Schema.Unknown; }>
schema
)(
const input: {}
input
)) // Output: false
8
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
(
import Schema
Schema
.
(alias) is<{ readonly a: unknown; }, { readonly a: unknown; }, never>(schema: Schema.Schema<{ readonly a: unknown; }, { readonly a: unknown; }, never>, options?: SchemaAST.ParseOptions): (u: unknown, overrideOptions?: SchemaAST.ParseOptions | number) => u is { readonly a: unknown; } export is

By default the option `exact` is set to `true`.

is
(
const schema: Schema.Struct<{ a: typeof Schema.Unknown; }>
schema
)(
const input: {}
input
, {
(property) ParseOptions.exact?: boolean | undefined

Handles missing properties in data structures. By default, missing properties are treated as if present with an `undefined` value. To treat missing properties as errors, set the `exact` option to `true`. This setting is already enabled by default for `is` and `asserts` functions, treating absent properties strictly unless overridden. default: false

exact
: false })) // Output: true
9
10
const
const asserts: (u: unknown, overrideOptions?: SchemaAST.ParseOptions) => asserts u is { readonly a: unknown; }
asserts
: (
11
(parameter) u: unknown
u
: unknown,
12
(parameter) overrideOptions: SchemaAST.ParseOptions | undefined
overrideOptions
?:
import SchemaAST
SchemaAST
.
interface ParseOptions
ParseOptions
13
) => asserts
(parameter) u: unknown
u
is {
14
readonly
(property) a: unknown
a
: unknown
15
} =
import Schema
Schema
.
(alias) asserts<{ readonly a: unknown; }, { readonly a: unknown; }, never>(schema: Schema.Schema<{ readonly a: unknown; }, { readonly a: unknown; }, never>, options?: SchemaAST.ParseOptions): (u: unknown, overrideOptions?: SchemaAST.ParseOptions) => asserts u is { readonly a: unknown; } export asserts

By default the option `exact` is set to `true`.

asserts
(
const schema: Schema.Struct<{ a: typeof Schema.Unknown; }>
schema
)
16
17
try {
18
const asserts: (u: unknown, overrideOptions?: SchemaAST.ParseOptions) => asserts u is { readonly a: unknown; }
asserts
(
const input: {}
input
)
19
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
("asserts passed")
20
} catch (
var e: any
e
: any) {
21
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.error(message?: any, ...optionalParams: any[]): void

Prints to `stderr` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const code = 5; console.error('error #%d', code); // Prints: error #5, to stderr console.error('error', code); // Prints: error 5, to stderr ``` If formatting elements (e.g. `%d`) are not found in the first string then [`util.inspect()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilinspectobject-options) is called on each argument and the resulting string values are concatenated. See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

error
("asserts failed")
22
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.error(message?: any, ...optionalParams: any[]): void

Prints to `stderr` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const code = 5; console.error('error #%d', code); // Prints: error #5, to stderr console.error('error', code); // Prints: error 5, to stderr ``` If formatting elements (e.g. `%d`) are not found in the first string then [`util.inspect()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilinspectobject-options) is called on each argument and the resulting string values are concatenated. See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

error
(
var e: any
e
.
any
message
)
23
}
24
/*
25
Output:
26
asserts failed
27
{ readonly a: unknown }
28
└─ ["a"]
29
└─ is missing
30
*/
31
32
try {
33
const asserts: (u: unknown, overrideOptions?: SchemaAST.ParseOptions) => asserts u is { readonly a: unknown; }
asserts
(
const input: {}
input
, {
(property) ParseOptions.exact?: boolean | undefined

Handles missing properties in data structures. By default, missing properties are treated as if present with an `undefined` value. To treat missing properties as errors, set the `exact` option to `true`. This setting is already enabled by default for `is` and `asserts` functions, treating absent properties strictly unless overridden. default: false

exact
: false })
34
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.log(message?: any, ...optionalParams: any[]): void

Prints to `stdout` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const count = 5; console.log('count: %d', count); // Prints: count: 5, to stdout console.log('count:', count); // Prints: count: 5, to stdout ``` See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

log
("asserts passed")
35
} catch (
var e: any
e
: any) {
36
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.error(message?: any, ...optionalParams: any[]): void

Prints to `stderr` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const code = 5; console.error('error #%d', code); // Prints: error #5, to stderr console.error('error', code); // Prints: error 5, to stderr ``` If formatting elements (e.g. `%d`) are not found in the first string then [`util.inspect()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilinspectobject-options) is called on each argument and the resulting string values are concatenated. See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

error
("asserts failed")
37
namespace console var console: Console

The `console` module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers. The module exports two specific components: * A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream. * A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and [`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module. _**Warning**_: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for more information. Example using the global `console`: ```js console.log('hello world'); // Prints: hello world, to stdout console.log('hello %s', 'world'); // Prints: hello world, to stdout console.error(new Error('Whoops, something bad happened')); // Prints error message and stack trace to stderr: // Error: Whoops, something bad happened // at [eval]:5:15 // at Script.runInThisContext (node:vm:132:18) // at Object.runInThisContext (node:vm:309:38) // at node:internal/process/execution:77:19 // at [eval]-wrapper:6:22 // at evalScript (node:internal/process/execution:76:60) // at node:internal/main/eval_string:23:3 const name = 'Will Robinson'; console.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to stderr ``` Example using the `Console` class: ```js const out = getStreamSomehow(); const err = getStreamSomehow(); const myConsole = new console.Console(out, err); myConsole.log('hello world'); // Prints: hello world, to out myConsole.log('hello %s', 'world'); // Prints: hello world, to out myConsole.error(new Error('Whoops, something bad happened')); // Prints: [Error: Whoops, something bad happened], to err const name = 'Will Robinson'; myConsole.warn(`Danger ${name}! Danger!`); // Prints: Danger Will Robinson! Danger!, to err ```

console
.
(method) Console.error(message?: any, ...optionalParams: any[]): void

Prints to `stderr` with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html) (the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)). ```js const code = 5; console.error('error #%d', code); // Prints: error #5, to stderr console.error('error', code); // Prints: error 5, to stderr ``` If formatting elements (e.g. `%d`) are not found in the first string then [`util.inspect()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilinspectobject-options) is called on each argument and the resulting string values are concatenated. See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.

error
(
var e: any
e
.
any
message
)
38
}
39
// Output: asserts passed

The naming conventions in effect/Schema are designed to be straightforward and logical, focusing primarily on compatibility with JSON serialization. This approach simplifies the understanding and use of schemas, especially for developers who are integrating web technologies where JSON is a standard data interchange format.

JSON-Compatible Types

Schemas that naturally serialize to JSON-compatible formats are named directly after their data types.

For instance:

  • Schema.Date: serializes JavaScript Date objects to ISO-formatted strings, a typical method for representing dates in JSON.
  • Schema.Number: used directly as it maps precisely to the JSON number type, requiring no special transformation to remain JSON-compatible.

Non-JSON-Compatible Types

When dealing with types that do not have a direct representation in JSON, the naming strategy incorporates additional details to indicate the necessary transformation. This helps in setting clear expectations about the schema’s behavior:

For instance:

  • Schema.DateFromSelf: indicates that the schema handles Date objects, which are not natively JSON-serializable.
  • Schema.NumberFromString: this naming suggests that the schema processes numbers that are initially represented as strings, emphasizing the transformation from string to number when decoding.

The primary goal of these schemas is to ensure that domain objects can be easily serialized (“encoded”) and deserialized (“decoded”) for transmission over network connections, thus facilitating their transfer between different parts of an application or across different applications.

While JSON’s ubiquity justifies its primary consideration in naming, the conventions also accommodate serialization for other types of transport. For instance, converting a Date to a string is a universally useful method for various communication protocols, not just JSON. Thus, the selected naming conventions serve as sensible defaults that prioritize clarity and ease of use, facilitating the serialization and deserialization processes across diverse technological environments.