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PubSub

A PubSub serves as an asynchronous message hub, allowing publishers to send messages that can be received by all current subscribers.

Unlike a Queue, where each value is delivered to only one consumer, a PubSub broadcasts each published message to all subscribers. This makes PubSub ideal for scenarios requiring message broadcasting rather than load distribution.

A PubSub<A> stores messages of type A and provides two fundamental operations:

APIDescription
PubSub.publishSends a message of type A to the PubSub, returning an effect indicating if the message was successfully published.
PubSub.subscribeCreates a scoped effect that allows subscription to the PubSub, automatically unsubscribing when the scope ends. Subscribers receive messages through a Dequeue which holds published messages.

Example (Publishing a Message to Multiple Subscribers)

1
import {
import Effect
Effect
,
import PubSub
PubSub
,
import Queue
Queue
} from "effect"
2
3
const
const program: Effect.Effect<void, never, never>
program
=
import Effect
Effect
.
const scoped: <void, never, Scope>(effect: Effect.Effect<void, never, Scope>) => Effect.Effect<void, never, never>

Scopes all resources used in this workflow to the lifetime of the workflow, ensuring that their finalizers are run as soon as this workflow completes execution, whether by success, failure, or interruption.

scoped
(
4
import Effect
Effect
.
const gen: <YieldWrap<Effect.Effect<PubSub.PubSub<string>, never, never>> | YieldWrap<Effect.Effect<Queue.Dequeue<string>, never, Scope>> | YieldWrap<...> | YieldWrap<...>, void>(f: (resume: Effect.Adapter) => Generator<...>) => Effect.Effect<...> (+1 overload)
gen
(function* () {
5
const
const pubsub: PubSub.PubSub<string>
pubsub
= yield*
import PubSub
PubSub
.
const bounded: <string>(capacity: number | { readonly capacity: number; readonly replay?: number | undefined; }) => Effect.Effect<PubSub.PubSub<string>, never, never>

Creates a bounded `PubSub` with the back pressure strategy. The `PubSub` will retain messages until they have been taken by all subscribers, applying back pressure to publishers if the `PubSub` is at capacity. For best performance use capacities that are powers of two.

bounded
<string>(2)
6
7
// Two subscribers
8
const
const dequeue1: Queue.Dequeue<string>
dequeue1
= yield*
import PubSub
PubSub
.
const subscribe: <string>(self: PubSub.PubSub<string>) => Effect.Effect<Queue.Dequeue<string>, never, Scope>

Subscribes to receive messages from the `PubSub`. The resulting subscription can be evaluated multiple times within the scope to take a message from the `PubSub` each time.

subscribe
(
const pubsub: PubSub.PubSub<string>
pubsub
)
9
const
const dequeue2: Queue.Dequeue<string>
dequeue2
= yield*
import PubSub
PubSub
.
const subscribe: <string>(self: PubSub.PubSub<string>) => Effect.Effect<Queue.Dequeue<string>, never, Scope>

Subscribes to receive messages from the `PubSub`. The resulting subscription can be evaluated multiple times within the scope to take a message from the `PubSub` each time.

subscribe
(
const pubsub: PubSub.PubSub<string>
pubsub
)
10
11
// Publish a message to the pubsub
12
yield*
import PubSub
PubSub
.
const publish: <string>(self: PubSub.PubSub<string>, value: string) => Effect.Effect<boolean> (+1 overload)

Publishes a message to the `PubSub`, returning whether the message was published to the `PubSub`.

publish
(
const pubsub: PubSub.PubSub<string>
pubsub
, "Hello from a PubSub!")
13
14
// Each subscriber receives the message
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
("Subscriber 1: " + (yield*
import Queue
Queue
.
const take: <string>(self: Queue.Dequeue<string>) => Effect.Effect<string, never, never>

Takes the oldest value in the queue. If the queue is empty, this will return a computation that resumes when an item has been added to the queue.

take
(
const dequeue1: Queue.Dequeue<string>
dequeue1
)))
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
("Subscriber 2: " + (yield*
import Queue
Queue
.
const take: <string>(self: Queue.Dequeue<string>) => Effect.Effect<string, never, never>

Takes the oldest value in the queue. If the queue is empty, this will return a computation that resumes when an item has been added to the queue.

take
(
const dequeue2: Queue.Dequeue<string>
dequeue2
)))
17
})
18
)
19
20
import Effect
Effect
.
const runFork: <void, never>(effect: Effect.Effect<void, never, never>, options?: RunForkOptions) => RuntimeFiber<void, never>

Executes an effect and returns a `RuntimeFiber` that represents the running computation. Use `runFork` when you want to start an effect without blocking the current execution flow. It returns a fiber that you can observe, interrupt, or join as needed.

runFork
(
const program: Effect.Effect<void, never, never>
program
)
21
/*
22
Output:
23
Subscriber 1: Hello from a PubSub!
24
Subscriber 2: Hello from a PubSub!
25
*/

A bounded PubSub applies back pressure to publishers when it reaches capacity, suspending additional publishing until space becomes available.

Back pressure ensures that all subscribers receive all messages while they are subscribed. However, it can lead to slower message delivery if a subscriber is slow.

Example (Bounded PubSub Creation)

1
import {
import PubSub
PubSub
} from "effect"
2
3
// Creates a bounded PubSub with a capacity of 2
4
const
const boundedPubSub: Effect<PubSub.PubSub<string>, never, never>
boundedPubSub
=
import PubSub
PubSub
.
const bounded: <string>(capacity: number | { readonly capacity: number; readonly replay?: number | undefined; }) => Effect<PubSub.PubSub<string>, never, never>

Creates a bounded `PubSub` with the back pressure strategy. The `PubSub` will retain messages until they have been taken by all subscribers, applying back pressure to publishers if the `PubSub` is at capacity. For best performance use capacities that are powers of two.

bounded
<string>(2)

A dropping PubSub discards new values when full. The PubSub.publish operation returns false if the message is dropped.

In a dropping pubsub, publishers can continue to publish new values, but subscribers are not guaranteed to receive all messages.

Example (Dropping PubSub Creation)

1
import {
import PubSub
PubSub
} from "effect"
2
3
// Creates a dropping PubSub with a capacity of 2
4
const
const droppingPubSub: Effect<PubSub.PubSub<string>, never, never>
droppingPubSub
=
import PubSub
PubSub
.
const dropping: <string>(capacity: number | { readonly capacity: number; readonly replay?: number | undefined; }) => Effect<PubSub.PubSub<string>, never, never>

Creates a bounded `PubSub` with the dropping strategy. The `PubSub` will drop new messages if the `PubSub` is at capacity. For best performance use capacities that are powers of two.

dropping
<string>(2)

A sliding PubSub removes the oldest message to make space for new ones, ensuring that publishing never blocks.

A sliding pubsub prevents slow subscribers from impacting the message delivery rate. However, there’s still a risk that slow subscribers may miss some messages.

Example (Sliding PubSub Creation)

1
import {
import PubSub
PubSub
} from "effect"
2
3
// Creates a sliding PubSub with a capacity of 2
4
const
const slidingPubSub: Effect<PubSub.PubSub<string>, never, never>
slidingPubSub
=
import PubSub
PubSub
.
const sliding: <string>(capacity: number | { readonly capacity: number; readonly replay?: number | undefined; }) => Effect<PubSub.PubSub<string>, never, never>

Creates a bounded `PubSub` with the sliding strategy. The `PubSub` will add new messages and drop old messages if the `PubSub` is at capacity. For best performance use capacities that are powers of two.

sliding
<string>(2)

An unbounded PubSub has no capacity limit, so publishing always succeeds immediately.

Unbounded pubsubs guarantee that all subscribers receive all messages without slowing down message delivery. However, they can grow indefinitely if messages are published faster than they are consumed.

Generally, it’s recommended to use bounded, dropping, or sliding pubsubs unless you have specific use cases for unbounded pubsubs.

Example

1
import {
import PubSub
PubSub
} from "effect"
2
3
// Creates an unbounded PubSub with unlimited capacity
4
const
const unboundedPubSub: Effect<PubSub.PubSub<string>, never, never>
unboundedPubSub
=
import PubSub
PubSub
.
const unbounded: <string>(options?: { readonly replay?: number | undefined; }) => Effect<PubSub.PubSub<string>, never, never>

Creates an unbounded `PubSub`.

unbounded
<string>()

The PubSub.publishAll function lets you publish multiple values to the pubsub at once.

Example (Publishing Multiple Messages)

1
import {
import Effect
Effect
,
import PubSub
PubSub
,
import Queue
Queue
} from "effect"
2
3
const
const program: Effect.Effect<void, never, never>
program
=
import Effect
Effect
.
const scoped: <void, never, Scope>(effect: Effect.Effect<void, never, Scope>) => Effect.Effect<void, never, never>

Scopes all resources used in this workflow to the lifetime of the workflow, ensuring that their finalizers are run as soon as this workflow completes execution, whether by success, failure, or interruption.

scoped
(
4
import Effect
Effect
.
const gen: <YieldWrap<Effect.Effect<PubSub.PubSub<string>, never, never>> | YieldWrap<Effect.Effect<Queue.Dequeue<string>, never, Scope>> | YieldWrap<...> | YieldWrap<...>, void>(f: (resume: Effect.Adapter) => Generator<...>) => Effect.Effect<...> (+1 overload)
gen
(function* () {
5
const
const pubsub: PubSub.PubSub<string>
pubsub
= yield*
import PubSub
PubSub
.
const bounded: <string>(capacity: number | { readonly capacity: number; readonly replay?: number | undefined; }) => Effect.Effect<PubSub.PubSub<string>, never, never>

Creates a bounded `PubSub` with the back pressure strategy. The `PubSub` will retain messages until they have been taken by all subscribers, applying back pressure to publishers if the `PubSub` is at capacity. For best performance use capacities that are powers of two.

bounded
<string>(2)
6
const
const dequeue: Queue.Dequeue<string>
dequeue
= yield*
import PubSub
PubSub
.
const subscribe: <string>(self: PubSub.PubSub<string>) => Effect.Effect<Queue.Dequeue<string>, never, Scope>

Subscribes to receive messages from the `PubSub`. The resulting subscription can be evaluated multiple times within the scope to take a message from the `PubSub` each time.

subscribe
(
const pubsub: PubSub.PubSub<string>
pubsub
)
7
yield*
import PubSub
PubSub
.
const publishAll: <string>(self: PubSub.PubSub<string>, elements: Iterable<string>) => Effect.Effect<boolean> (+1 overload)

Publishes all of the specified messages to the `PubSub`, returning whether they were published to the `PubSub`.

publishAll
(
const pubsub: PubSub.PubSub<string>
pubsub
, ["Message 1", "Message 2"])
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
(yield*
import Queue
Queue
.
const takeAll: <string>(self: Queue.Dequeue<string>) => Effect.Effect<Chunk<string>, never, never>

Takes all the values in the queue and returns the values. If the queue is empty returns an empty collection.

takeAll
(
const dequeue: Queue.Dequeue<string>
dequeue
))
9
})
10
)
11
12
import Effect
Effect
.
const runFork: <void, never>(effect: Effect.Effect<void, never, never>, options?: RunForkOptions) => RuntimeFiber<void, never>

Executes an effect and returns a `RuntimeFiber` that represents the running computation. Use `runFork` when you want to start an effect without blocking the current execution flow. It returns a fiber that you can observe, interrupt, or join as needed.

runFork
(
const program: Effect.Effect<void, never, never>
program
)
13
/*
14
Output:
15
{ _id: 'Chunk', values: [ 'Message 1', 'Message 2' ] }
16
*/

You can check the capacity and current size of a pubsub using PubSub.capacity and PubSub.size, respectively.

Note that PubSub.capacity returns a number because the capacity is set at pubsub creation and never changes. In contrast, PubSub.size returns an effect that determines the current size of the pubsub since the number of messages in the pubsub can change over time.

Example (Retrieving PubSub Capacity and Size)

1
import {
import Effect
Effect
,
import PubSub
PubSub
} from "effect"
2
3
const
const program: Effect.Effect<void, never, never>
program
=
import Effect
Effect
.
const gen: <YieldWrap<Effect.Effect<PubSub.PubSub<number>, never, never>> | YieldWrap<Effect.Effect<number, never, never>>, void>(f: (resume: Effect.Adapter) => Generator<...>) => Effect.Effect<...> (+1 overload)
gen
(function* () {
4
const
const pubsub: PubSub.PubSub<number>
pubsub
= yield*
import PubSub
PubSub
.
const bounded: <number>(capacity: number | { readonly capacity: number; readonly replay?: number | undefined; }) => Effect.Effect<PubSub.PubSub<number>, never, never>

Creates a bounded `PubSub` with the back pressure strategy. The `PubSub` will retain messages until they have been taken by all subscribers, applying back pressure to publishers if the `PubSub` is at capacity. For best performance use capacities that are powers of two.

bounded
<number>(2)
5
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
(`capacity: ${
import PubSub
PubSub
.
const capacity: <number>(self: PubSub.PubSub<number>) => number

Returns the number of elements the queue can hold.

capacity
(
const pubsub: PubSub.PubSub<number>
pubsub
)}`)
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
(`size: ${yield*
import PubSub
PubSub
.
const size: <number>(self: PubSub.PubSub<number>) => Effect.Effect<number>

Retrieves the size of the queue, which is equal to the number of elements in the queue. This may be negative if fibers are suspended waiting for elements to be added to the queue.

size
(
const pubsub: PubSub.PubSub<number>
pubsub
)}`)
7
})
8
9
import Effect
Effect
.
const runFork: <void, never>(effect: Effect.Effect<void, never, never>, options?: RunForkOptions) => RuntimeFiber<void, never>

Executes an effect and returns a `RuntimeFiber` that represents the running computation. Use `runFork` when you want to start an effect without blocking the current execution flow. It returns a fiber that you can observe, interrupt, or join as needed.

runFork
(
const program: Effect.Effect<void, never, never>
program
)
10
/*
11
Output:
12
capacity: 2
13
size: 0
14
*/

To shut down a pubsub, use PubSub.shutdown. You can also verify if it has been shut down with PubSub.isShutdown, or wait for the shutdown to complete with PubSub.awaitShutdown. Shutting down a pubsub also terminates all associated queues, ensuring that the shutdown signal is effectively communicated.

PubSub operators mirror those of Queue with the main difference being that PubSub.publish and PubSub.subscribe are used in place of Queue.offer and Queue.take. If you’re already familiar with using a Queue, you’ll find PubSub straightforward.

Essentially, a PubSub can be seen as a Enqueue that only allows writes:

import type {
import Queue
Queue
} from "effect"
interface
interface PubSub<A>
PubSub
<
(type parameter) A in PubSub<A>
A
> extends
import Queue
Queue
.
interface Enqueue<in A>
Enqueue
<
(type parameter) A in PubSub<A>
A
> {}

Here, the Enqueue type refers to a queue that only accepts enqueues (or writes). Any value enqueued here is published to the pubsub, and operations like shutdown will also affect the pubsub.

This design makes PubSub highly flexible, letting you use it anywhere you need a Enqueue that only accepts published values.