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Effect vs Promise

In this guide, we will explore the differences between Promise and Effect, two approaches to handling asynchronous operations in TypeScript. We’ll discuss their type safety, creation, chaining, and concurrency, providing examples to help you understand their usage.

  • Evaluation Strategy: Promises are eagerly evaluated, whereas effects are lazily evaluated.
  • Execution Mode: Promises are one-shot, executing once, while effects are multi-shot, repeatable.
  • Interruption Handling and Automatic Propagation: Promises lack built-in interruption handling, posing challenges in managing interruptions, and don’t automatically propagate interruptions, requiring manual abort controller management. In contrast, effects come with interruption handling capabilities and automatically compose interruption, simplifying management locally on smaller computations without the need for high-level orchestration.
  • Structured Concurrency: Effects offer structured concurrency built-in, which is challenging to achieve with Promises.
  • Error Reporting (Type Safety): Promises don’t inherently provide detailed error reporting at the type level, whereas effects do, offering type-safe insight into error cases.
  • Runtime Behavior: The Effect runtime aims to remain synchronous as long as possible, transitioning into asynchronous mode only when necessary due to computation requirements or main thread starvation.

Let’s start by comparing the types of Promise and Effect. The type parameter A represents the resolved value of the operation:

Promise<A>

Here’s what sets Effect apart:

  • It allows you to track the types of errors statically through the type parameter Error. For more information about error management in Effect, see Expected Errors.
  • It allows you to track the types of required dependencies statically through the type parameter Context. For more information about context management in Effect, see Managing Services.

Let’s compare creating a successful operation using Promise and Effect:

const
const success: Promise<number>
success
=
var Promise: PromiseConstructor

Represents the completion of an asynchronous operation

Promise
.
PromiseConstructor.resolve<number>(value: number): Promise<number> (+2 overloads)

Creates a new resolved promise for the provided value.

@paramvalue A promise.

@returnsA promise whose internal state matches the provided promise.

resolve
(2)

Now, let’s see how to handle failures with Promise and Effect:

const
const failure: Promise<never>
failure
=
var Promise: PromiseConstructor

Represents the completion of an asynchronous operation

Promise
.
PromiseConstructor.reject<never>(reason?: any): Promise<never>

Creates a new rejected promise for the provided reason.

@paramreason The reason the promise was rejected.

@returnsA new rejected Promise.

reject
("Uh oh!")

Creating operations with custom logic:

const
const task: Promise<number>
task
= new
var Promise: PromiseConstructor
new <number>(executor: (resolve: (value: number | PromiseLike<number>) => void, reject: (reason?: any) => void) => void) => Promise<number>

Creates a new Promise.

@paramexecutor A callback used to initialize the promise. This callback is passed two arguments: a resolve callback used to resolve the promise with a value or the result of another promise, and a reject callback used to reject the promise with a provided reason or error.

Promise
<number>((
resolve: (value: number | PromiseLike<number>) => void
resolve
,
reject: (reason?: any) => void
reject
) => {
function setTimeout<[]>(callback: () => void, ms?: number): NodeJS.Timeout (+1 overload)

Schedules execution of a one-time callback after delay milliseconds.

The callback will likely not be invoked in precisely delay milliseconds. Node.js makes no guarantees about the exact timing of when callbacks will fire, nor of their ordering. The callback will be called as close as possible to the time specified.

When delay is larger than 2147483647 or less than 1, the delay will be set to 1. Non-integer delays are truncated to an integer.

If callback is not a function, a TypeError will be thrown.

This method has a custom variant for promises that is available using timersPromises.setTimeout().

@sincev0.0.1

@paramcallback The function to call when the timer elapses.

@paramdelay The number of milliseconds to wait before calling the callback.

@paramargs Optional arguments to pass when the callback is called.

setTimeout
(() => {
var Math: Math

An intrinsic object that provides basic mathematics functionality and constants.

Math
.
Math.random(): number

Returns a pseudorandom number between 0 and 1.

random
() > 0.5 ?
resolve: (value: number | PromiseLike<number>) => void
resolve
(2) :
reject: (reason?: any) => void
reject
("Uh oh!")
}, 300)
})

Mapping the result of an operation:

const
const mapped: Promise<number>
mapped
=
var Promise: PromiseConstructor

Represents the completion of an asynchronous operation

Promise
.
PromiseConstructor.resolve<string>(value: string): Promise<string> (+2 overloads)

Creates a new resolved promise for the provided value.

@paramvalue A promise.

@returnsA promise whose internal state matches the provided promise.

resolve
("Hello").
Promise<string>.then<number, never>(onfulfilled?: ((value: string) => number | PromiseLike<number>) | null | undefined, onrejected?: ((reason: any) => PromiseLike<never>) | null | undefined): Promise<...>

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

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA Promise for the completion of which ever callback is executed.

then
((
s: string
s
) =>
s: string
s
.
String.length: number

Returns the length of a String object.

length
)

Chaining multiple operations:

const
const flatMapped: Promise<number>
flatMapped
=
var Promise: PromiseConstructor

Represents the completion of an asynchronous operation

Promise
.
PromiseConstructor.resolve<string>(value: string): Promise<string> (+2 overloads)

Creates a new resolved promise for the provided value.

@paramvalue A promise.

@returnsA promise whose internal state matches the provided promise.

resolve
("Hello").
Promise<string>.then<number, never>(onfulfilled?: ((value: string) => number | PromiseLike<number>) | null | undefined, onrejected?: ((reason: any) => PromiseLike<never>) | null | undefined): Promise<...>

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

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA Promise for the completion of which ever callback is executed.

then
((
s: string
s
) =>
var Promise: PromiseConstructor

Represents the completion of an asynchronous operation

Promise
.
PromiseConstructor.resolve<number>(value: number): Promise<number> (+2 overloads)

Creates a new resolved promise for the provided value.

@paramvalue A promise.

@returnsA promise whose internal state matches the provided promise.

resolve
(
s: string
s
.
String.length: number

Returns the length of a String object.

length
)
)

If you are familiar with async/await, you may notice that the flow of writing code is similar.

Let’s compare the two approaches:

const
const increment: (x: number) => number
increment
= (
x: number
x
: number) =>
x: number
x
+ 1
const
const divide: (a: number, b: number) => Promise<number>
divide
= (
a: number
a
: number,
b: number
b
: number):
interface Promise<T>

Represents the completion of an asynchronous operation

Promise
<number> =>
b: number
b
=== 0
?
var Promise: PromiseConstructor

Represents the completion of an asynchronous operation

Promise
.
PromiseConstructor.reject<number>(reason?: any): Promise<number>

Creates a new rejected promise for the provided reason.

@paramreason The reason the promise was rejected.

@returnsA new rejected Promise.

reject
(new
var Error: ErrorConstructor
new (message?: string) => Error
Error
("Cannot divide by zero"))
:
var Promise: PromiseConstructor

Represents the completion of an asynchronous operation

Promise
.
PromiseConstructor.resolve<number>(value: number): Promise<number> (+2 overloads)

Creates a new resolved promise for the provided value.

@paramvalue A promise.

@returnsA promise whose internal state matches the provided promise.

resolve
(
a: number
a
/
b: number
b
)
const
const task1: Promise<number>
task1
=
var Promise: PromiseConstructor

Represents the completion of an asynchronous operation

Promise
.
PromiseConstructor.resolve<number>(value: number): Promise<number> (+2 overloads)

Creates a new resolved promise for the provided value.

@paramvalue A promise.

@returnsA promise whose internal state matches the provided promise.

resolve
(10)
const
const task2: Promise<number>
task2
=
var Promise: PromiseConstructor

Represents the completion of an asynchronous operation

Promise
.
PromiseConstructor.resolve<number>(value: number): Promise<number> (+2 overloads)

Creates a new resolved promise for the provided value.

@paramvalue A promise.

@returnsA promise whose internal state matches the provided promise.

resolve
(2)
const
const program: () => Promise<string>
program
= async function () {
const
const a: number
a
= await
const task1: Promise<number>
task1
const
const b: number
b
= await
const task2: Promise<number>
task2
const
const n1: number
n1
= await
const divide: (a: number, b: number) => Promise<number>
divide
(
const a: number
a
,
const b: number
b
)
const
const n2: number
n2
=
const increment: (x: number) => number
increment
(
const n1: number
n1
)
return `Result is: ${
const n2: number
n2
}`
}
const program: () => Promise<string>
program
().
Promise<string>.then<void, never>(onfulfilled?: ((value: string) => void | PromiseLike<void>) | null | undefined, onrejected?: ((reason: any) => PromiseLike<never>) | null | undefined): Promise<...>

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

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA Promise for the completion of which ever callback is executed.

then
(
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 and process.stderr. 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 for more information.

Example using the global console:

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:

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

@seesource

console
.
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) (the arguments are all passed to util.format()).

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() for more information.

@sincev0.1.100

log
) // Output: "Result is: 6"

It’s important to note that although the code appears similar, the two programs are not identical. The purpose of comparing them side by side is just to highlight the resemblance in how they are written.

const
const task1: Promise<number>
task1
= new
var Promise: PromiseConstructor
new <number>(executor: (resolve: (value: number | PromiseLike<number>) => void, reject: (reason?: any) => void) => void) => Promise<number>

Creates a new Promise.

@paramexecutor A callback used to initialize the promise. This callback is passed two arguments: a resolve callback used to resolve the promise with a value or the result of another promise, and a reject callback used to reject the promise with a provided reason or error.

Promise
<number>((
resolve: (value: number | PromiseLike<number>) => void
resolve
,
reject: (reason?: any) => void
reject
) => {
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 and process.stderr. 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 for more information.

Example using the global console:

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:

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

@seesource

console
.
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) (the arguments are all passed to util.format()).

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() for more information.

@sincev0.1.100

log
("Executing task1...")
function setTimeout<[]>(callback: () => void, ms?: number): NodeJS.Timeout (+1 overload)

Schedules execution of a one-time callback after delay milliseconds.

The callback will likely not be invoked in precisely delay milliseconds. Node.js makes no guarantees about the exact timing of when callbacks will fire, nor of their ordering. The callback will be called as close as possible to the time specified.

When delay is larger than 2147483647 or less than 1, the delay will be set to 1. Non-integer delays are truncated to an integer.

If callback is not a function, a TypeError will be thrown.

This method has a custom variant for promises that is available using timersPromises.setTimeout().

@sincev0.0.1

@paramcallback The function to call when the timer elapses.

@paramdelay The number of milliseconds to wait before calling the callback.

@paramargs Optional arguments to pass when the callback is called.

setTimeout
(() => {
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 and process.stderr. 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 for more information.

Example using the global console:

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:

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

@seesource

console
.
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) (the arguments are all passed to util.format()).

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() for more information.

@sincev0.1.100

log
("task1 done")
resolve: (value: number | PromiseLike<number>) => void
resolve
(1)
}, 100)
})
const
const task2: Promise<number>
task2
= new
var Promise: PromiseConstructor
new <number>(executor: (resolve: (value: number | PromiseLike<number>) => void, reject: (reason?: any) => void) => void) => Promise<number>

Creates a new Promise.

@paramexecutor A callback used to initialize the promise. This callback is passed two arguments: a resolve callback used to resolve the promise with a value or the result of another promise, and a reject callback used to reject the promise with a provided reason or error.

Promise
<number>((
resolve: (value: number | PromiseLike<number>) => void
resolve
,
reject: (reason?: any) => void
reject
) => {
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 and process.stderr. 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 for more information.

Example using the global console:

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:

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

@seesource

console
.
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) (the arguments are all passed to util.format()).

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() for more information.

@sincev0.1.100

log
("Executing task2...")
function setTimeout<[]>(callback: () => void, ms?: number): NodeJS.Timeout (+1 overload)

Schedules execution of a one-time callback after delay milliseconds.

The callback will likely not be invoked in precisely delay milliseconds. Node.js makes no guarantees about the exact timing of when callbacks will fire, nor of their ordering. The callback will be called as close as possible to the time specified.

When delay is larger than 2147483647 or less than 1, the delay will be set to 1. Non-integer delays are truncated to an integer.

If callback is not a function, a TypeError will be thrown.

This method has a custom variant for promises that is available using timersPromises.setTimeout().

@sincev0.0.1

@paramcallback The function to call when the timer elapses.

@paramdelay The number of milliseconds to wait before calling the callback.

@paramargs Optional arguments to pass when the callback is called.

setTimeout
(() => {
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 and process.stderr. 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 for more information.

Example using the global console:

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:

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

@seesource

console
.
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) (the arguments are all passed to util.format()).

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() for more information.

@sincev0.1.100

log
("task2 done")
reject: (reason?: any) => void
reject
("Uh oh!")
}, 200)
})
const
const task3: Promise<number>
task3
= new
var Promise: PromiseConstructor
new <number>(executor: (resolve: (value: number | PromiseLike<number>) => void, reject: (reason?: any) => void) => void) => Promise<number>

Creates a new Promise.

@paramexecutor A callback used to initialize the promise. This callback is passed two arguments: a resolve callback used to resolve the promise with a value or the result of another promise, and a reject callback used to reject the promise with a provided reason or error.

Promise
<number>((
resolve: (value: number | PromiseLike<number>) => void
resolve
,
reject: (reason?: any) => void
reject
) => {
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 and process.stderr. 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 for more information.

Example using the global console:

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:

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

@seesource

console
.
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) (the arguments are all passed to util.format()).

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() for more information.

@sincev0.1.100

log
("Executing task3...")
function setTimeout<[]>(callback: () => void, ms?: number): NodeJS.Timeout (+1 overload)

Schedules execution of a one-time callback after delay milliseconds.

The callback will likely not be invoked in precisely delay milliseconds. Node.js makes no guarantees about the exact timing of when callbacks will fire, nor of their ordering. The callback will be called as close as possible to the time specified.

When delay is larger than 2147483647 or less than 1, the delay will be set to 1. Non-integer delays are truncated to an integer.

If callback is not a function, a TypeError will be thrown.

This method has a custom variant for promises that is available using timersPromises.setTimeout().

@sincev0.0.1

@paramcallback The function to call when the timer elapses.

@paramdelay The number of milliseconds to wait before calling the callback.

@paramargs Optional arguments to pass when the callback is called.

setTimeout
(() => {
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 and process.stderr. 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 for more information.

Example using the global console:

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:

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

@seesource

console
.
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) (the arguments are all passed to util.format()).

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() for more information.

@sincev0.1.100

log
("task3 done")
resolve: (value: number | PromiseLike<number>) => void
resolve
(3)
}, 300)
})
const
const program: Promise<[number, number, number]>
program
=
var Promise: PromiseConstructor

Represents the completion of an asynchronous operation

Promise
.
PromiseConstructor.all<[Promise<number>, Promise<number>, Promise<number>]>(values: [Promise<number>, Promise<number>, Promise<number>]): Promise<...> (+1 overload)

Creates a Promise that is resolved with an array of results when all of the provided Promises resolve, or rejected when any Promise is rejected.

@paramvalues An array of Promises.

@returnsA new Promise.

all
([
const task1: Promise<number>
task1
,
const task2: Promise<number>
task2
,
const task3: Promise<number>
task3
])
const program: Promise<[number, number, number]>
program
.
Promise<[number, number, number]>.then<void, void>(onfulfilled?: ((value: [number, number, number]) => void | PromiseLike<void>) | null | undefined, onrejected?: ((reason: any) => void | PromiseLike<void>) | null | undefined): Promise<...>

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

@paramonfulfilled The callback to execute when the Promise is resolved.

@paramonrejected The callback to execute when the Promise is rejected.

@returnsA Promise for the completion of which ever callback is executed.

then
(
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 and process.stderr. 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 for more information.

Example using the global console:

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:

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

@seesource

console
.
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) (the arguments are all passed to util.format()).

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() for more information.

@sincev0.1.100

log
,
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 and process.stderr. 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 for more information.

Example using the global console:

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:

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

@seesource

console
.
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) (the arguments are all passed to util.format()).

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() is called on each argument and the resulting string values are concatenated. See util.format() for more information.

@sincev0.1.100

error
)
/*
Output:
Executing task1...
Executing task2...
Executing task3...
task1 done
task2 done
Uh oh!
task3 done
*/
const task1 = new Promise<number>((resolve, reject) => {
console.log("Executing task1...")
setTimeout(() => {
console.log("task1 done")
resolve(1)
}, 100)
})
const task2 = new Promise<number>((resolve, reject) => {
console.log("Executing task2...")
setTimeout(() => {
console.log("task2 done")
reject("Uh oh!")
}, 200)
})
const task3 = new Promise<number>((resolve, reject) => {
console.log("Executing task3...")
setTimeout(() => {
console.log("task3 done")
resolve(3)
}, 300)
})
const program = Promise.allSettled([task1, task2, task3])
program.then(console.log, console.error)
/*
Output:
Executing task1...
Executing task2...
Executing task3...
task1 done
task2 done
task3 done
[
{ status: 'fulfilled', value: 1 },
{ status: 'rejected', reason: 'Uh oh!' },
{ status: 'fulfilled', value: 3 }
]
*/