delphirtl
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RTL functions from Delphi
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[**delphirtl**](../README.md) • **Docs**
***
[delphirtl](../globals.md) / Worker
Class: Worker
The `Worker` class represents an independent JavaScript execution thread.
Most Node.js APIs are available inside of it.
Notable differences inside a Worker environment are:
* The `process.stdin`, `process.stdout` and `process.stderr` may be redirected by the parent thread.
* The `require('worker_threads').isMainThread` property is set to `false`.
* The `require('worker_threads').parentPort` message port is available.
* `process.exit()` does not stop the whole program, just the single thread,
and `process.abort()` is not available.
* `process.chdir()` and `process` methods that set group or user ids
are not available.
* `process.env` is a copy of the parent thread's environment variables,
unless otherwise specified. Changes to one copy are not visible in other
threads, and are not visible to native add-ons (unless `worker.SHARE_ENV` is passed as the `env` option to the `Worker` constructor).
* `process.title` cannot be modified.
* Signals are not delivered through `process.on('...')`.
* Execution may stop at any point as a result of `worker.terminate()` being invoked.
* IPC channels from parent processes are not accessible.
* The `trace_events` module is not supported.
* Native add-ons can only be loaded from multiple threads if they fulfill `certain conditions`.
Creating `Worker` instances inside of other `Worker`s is possible.
Like [Web Workers](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API) and the `cluster module`, two-way communication can be
achieved through inter-thread message passing. Internally, a `Worker` has a
built-in pair of `MessagePort` s that are already associated with each other
when the `Worker` is created. While the `MessagePort` object on the parent side
is not directly exposed, its functionalities are exposed through `worker.postMessage()` and the `worker.on('message')` event
on the `Worker` object for the parent thread.
To create custom messaging channels (which is encouraged over using the default
global channel because it facilitates separation of concerns), users can create
a `MessageChannel` object on either thread and pass one of the`MessagePort`s on that `MessageChannel` to the other thread through a
pre-existing channel, such as the global one.
See `port.postMessage()` for more information on how messages are passed,
and what kind of JavaScript values can be successfully transported through
the thread barrier.
```js
const assert = require('assert');
const {
Worker, MessageChannel, MessagePort, isMainThread, parentPort
} = require('worker_threads');
if (isMainThread) {
const worker = new Worker(__filename);
const subChannel = new MessageChannel();
worker.postMessage({ hereIsYourPort: subChannel.port1 }, [subChannel.port1]);
subChannel.port2.on('message', (value) => {
console.log('received:', value);
});
} else {
parentPort.once('message', (value) => {
assert(value.hereIsYourPort instanceof MessagePort);
value.hereIsYourPort.postMessage('the worker is sending this');
value.hereIsYourPort.close();
});
}
```
# Since
v10.5.0
# Extends
- `EventEmitter`
# Constructors
## new Worker()
**new Worker**(`filename`, `options`?): [`Worker`](Worker.md)
### Parameters
• **filename**: `string` \| `URL`
The path to the Worker’s main script or module.
Must be either an absolute path or a relative path (i.e. relative to the current working directory) starting with ./ or ../,
or a WHATWG URL object using file: protocol. If options.eval is true, this is a string containing JavaScript code rather than a path.
• **options?**: `WorkerOptions`
### Returns
[`Worker`](Worker.md)
### Overrides
`EventEmitter.constructor`
### Defined in
node\_modules/@types/node/worker\_threads.d.ts:395
# Properties
## performance
`readonly` **performance**: `WorkerPerformance`
An object that can be used to query performance information from a worker
instance. Similar to `perf_hooks.performance`.
### Since
v15.1.0, v14.17.0, v12.22.0
### Defined in
node\_modules/@types/node/worker\_threads.d.ts:389
***
## resourceLimits?
`readonly` `optional` **resourceLimits**: `ResourceLimits`
Provides the set of JS engine resource constraints for this Worker thread.
If the `resourceLimits` option was passed to the `Worker` constructor,
this matches its values.
If the worker has stopped, the return value is an empty object.
### Since
v13.2.0, v12.16.0
### Defined in
node\_modules/@types/node/worker\_threads.d.ts:383
***
## stderr
`readonly` **stderr**: `Readable`
This is a readable stream which contains data written to `process.stderr` inside the worker thread. If `stderr: true` was not passed to the `Worker` constructor, then data is piped to the
parent thread's `process.stderr` stream.
### Since
v10.5.0
### Defined in
node\_modules/@types/node/worker\_threads.d.ts:367
***
## stdin
`readonly` **stdin**: `null` \| `Writable`
If `stdin: true` was passed to the `Worker` constructor, this is a
writable stream. The data written to this stream will be made available in
the worker thread as `process.stdin`.
### Since
v10.5.0
### Defined in
node\_modules/@types/node/worker\_threads.d.ts:355
***
## stdout
`readonly` **stdout**: `Readable`
This is a readable stream which contains data written to `process.stdout` inside the worker thread. If `stdout: true` was not passed to the `Worker` constructor, then data is piped to the
parent thread's `process.stdout` stream.
### Since
v10.5.0
### Defined in
node\_modules/@types/node/worker\_threads.d.ts:361
***
## threadId
`readonly` **threadId**: `number`
An integer identifier for the referenced thread. Inside the worker thread,
it is available as `require('worker_threads').threadId`.
This value is unique for each `Worker` instance inside a single process.
### Since
v10.5.0
### Defined in
node\_modules/@types/node/worker\_threads.d.ts:374
***
## captureRejections
`static` **captureRejections**: `boolean`
Sets or gets the default captureRejection value for all emitters.
### Inherited from
`EventEmitter.captureRejections`
### Defined in
node\_modules/@types/node/events.d.ts:306
***
## captureRejectionSymbol
`readonly` `static` **captureRejectionSymbol**: *typeof* [`captureRejectionSymbol`](Worker.md#capturerejectionsymbol)
### Inherited from
`EventEmitter.captureRejectionSymbol`
### Defined in
node\_modules/@types/node/events.d.ts:301
***
## defaultMaxListeners
`static` **defaultMaxListeners**: `number`
### Inherited from
`EventEmitter.defaultMaxListeners`
### Defined in
node\_modules/@types/node/events.d.ts:307
***
## errorMonitor
`readonly` `static` **errorMonitor**: *typeof* [`errorMonitor`](Worker.md#errormonitor)
This symbol shall be used to install a listener for only monitoring `'error'`
events. Listeners installed using this symbol are called before the regular
`'error'` listeners are called.
Installing a listener using this symbol does not change the behavior once an
`'error'` event is emitted, therefore the process will still crash if no
regular `'error'` listener is installed.
### Inherited from
`EventEmitter.errorMonitor`
### Defined in
node\_modules/@types/node/events.d.ts:300
# Methods
## addListener()
### addListener(event, listener)
**addListener**(`event`, `listener`): `this`
Alias for `emitter.on(eventName, listener)`.
#### Parameters
• **event**: `"error"`
• **listener**
#### Returns
`this`
#### Since
v0.1.26
#### Overrides
`EventEmitter.addListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:431
### addListener(event, listener)
**addListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"exit"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.addListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:432
### addListener(event, listener)
**addListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"message"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.addListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:433
### addListener(event, listener)
**addListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"messageerror"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.addListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:434
### addListener(event, listener)
**addListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"online"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.addListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:435
### addListener(event, listener)
**addListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `string` \| `symbol`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.addListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:436
***
## emit()
### emit(event, err)
**emit**(`event`, `err`): `boolean`
Synchronously calls each of the listeners registered for the event named`eventName`, in the order they were registered, passing the supplied arguments
to each.
Returns `true` if the event had listeners, `false` otherwise.
```js
const EventEmitter = require('events');
const myEmitter = new EventEmitter();
// First listener
myEmitter.on('event', function firstListener() {
console.log('Helloooo! first listener');
});
// Second listener
myEmitter.on('event', function secondListener(arg1, arg2) {
console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
});
// Third listener
myEmitter.on('event', function thirdListener(...args) {
const parameters = args.join(', ');
console.log(`event with parameters ${parameters} in third listener`);
});
console.log(myEmitter.listeners('event'));
myEmitter.emit('event', 1, 2, 3, 4, 5);
// Prints:
// [
// [Function: firstListener],
// [Function: secondListener],
// [Function: thirdListener]
// ]
// Helloooo! first listener
// event with parameters 1, 2 in second listener
// event with parameters 1, 2, 3, 4, 5 in third listener
```
#### Parameters
• **event**: `"error"`
• **err**: `Error`
#### Returns
`boolean`
#### Since
v0.1.26
#### Overrides
`EventEmitter.emit`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:437
### emit(event, exitCode)
**emit**(`event`, `exitCode`): `boolean`
#### Parameters
• **event**: `"exit"`
• **exitCode**: `number`
#### Returns
`boolean`
#### Overrides
`EventEmitter.emit`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:438
### emit(event, value)
**emit**(`event`, `value`): `boolean`
#### Parameters
• **event**: `"message"`
• **value**: `any`
#### Returns
`boolean`
#### Overrides
`EventEmitter.emit`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:439
### emit(event, error)
**emit**(`event`, `error`): `boolean`
#### Parameters
• **event**: `"messageerror"`
• **error**: `Error`
#### Returns
`boolean`
#### Overrides
`EventEmitter.emit`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:440
### emit(event)
**emit**(`event`): `boolean`
#### Parameters
• **event**: `"online"`
#### Returns
`boolean`
#### Overrides
`EventEmitter.emit`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:441
### emit(event, args)
**emit**(`event`, ...`args`): `boolean`
#### Parameters
• **event**: `string` \| `symbol`
• ...**args**: `any`[]
#### Returns
`boolean`
#### Overrides
`EventEmitter.emit`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:442
***
## eventNames()
**eventNames**(): (`string` \| `symbol`)[]
Returns an array listing the events for which the emitter has registered
listeners. The values in the array are strings or `Symbol`s.
```js
const EventEmitter = require('events');
const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});
const sym = Symbol('symbol');
myEE.on(sym, () => {});
console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]
```
### Returns
(`string` \| `symbol`)[]
### Since
v6.0.0
### Inherited from
`EventEmitter.eventNames`
### Defined in
node\_modules/@types/node/events.d.ts:642
***
## getHeapSnapshot()
**getHeapSnapshot**(): `Promise`\<`Readable`\>
Returns a readable stream for a V8 snapshot of the current state of the Worker.
See `v8.getHeapSnapshot()` for more details.
If the Worker thread is no longer running, which may occur before the `'exit' event` is emitted, the returned `Promise` is rejected
immediately with an `ERR_WORKER_NOT_RUNNING` error.
### Returns
`Promise`\<`Readable`\>
A promise for a Readable Stream containing a V8 heap snapshot
### Since
v13.9.0, v12.17.0
### Defined in
node\_modules/@types/node/worker\_threads.d.ts:430
***
## getMaxListeners()
**getMaxListeners**(): `number`
Returns the current max listener value for the `EventEmitter` which is either
set by `emitter.setMaxListeners(n)` or defaults to [defaultMaxListeners](Worker.md#defaultmaxlisteners).
### Returns
`number`
### Since
v1.0.0
### Inherited from
`EventEmitter.getMaxListeners`
### Defined in
node\_modules/@types/node/events.d.ts:499
***
## listenerCount()
**listenerCount**(`eventName`): `number`
Returns the number of listeners listening to the event named `eventName`.
### Parameters
• **eventName**: `string` \| `symbol`
The name of the event being listened for
### Returns
`number`
### Since
v3.2.0
### Inherited from
`EventEmitter.listenerCount`
### Defined in
node\_modules/@types/node/events.d.ts:589
***
## listeners()
**listeners**(`eventName`): `Function`[]
Returns a copy of the array of listeners for the event named `eventName`.
```js
server.on('connection', (stream) => {
console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
```
### Parameters
• **eventName**: `string` \| `symbol`
### Returns
`Function`[]
### Since
v0.1.26
### Inherited from
`EventEmitter.listeners`
### Defined in
node\_modules/@types/node/events.d.ts:512
***
## off()
### off(event, listener)
**off**(`event`, `listener`): `this`
Alias for `emitter.removeListener()`.
#### Parameters
• **event**: `"error"`
• **listener**
#### Returns
`this`
#### Since
v10.0.0
#### Overrides
`EventEmitter.off`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:473
### off(event, listener)
**off**(`event`, `listener`): `this`
#### Parameters
• **event**: `"exit"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.off`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:474
### off(event, listener)
**off**(`event`, `listener`): `this`
#### Parameters
• **event**: `"message"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.off`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:475
### off(event, listener)
**off**(`event`, `listener`): `this`
#### Parameters
• **event**: `"messageerror"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.off`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:476
### off(event, listener)
**off**(`event`, `listener`): `this`
#### Parameters
• **event**: `"online"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.off`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:477
### off(event, listener)
**off**(`event`, `listener`): `this`
#### Parameters
• **event**: `string` \| `symbol`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.off`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:478
***
## on()
### on(event, listener)
**on**(`event`, `listener`): `this`
Adds the `listener` function to the end of the listeners array for the
event named `eventName`. No checks are made to see if the `listener` has
already been added. Multiple calls passing the same combination of `eventName`and `listener` will result in the `listener` being added, and called, multiple
times.
```js
server.on('connection', (stream) => {
console.log('someone connected!');
});
```
Returns a reference to the `EventEmitter`, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The`emitter.prependListener()` method can be used as an alternative to add the
event listener to the beginning of the listeners array.
```js
const myEE = new EventEmitter();
myEE.on('foo', () => console.log('a'));
myEE.prependListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
```
#### Parameters
• **event**: `"error"`
• **listener**
The callback function
#### Returns
`this`
#### Since
v0.1.101
#### Overrides
`EventEmitter.on`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:443
### on(event, listener)
**on**(`event`, `listener`): `this`
#### Parameters
• **event**: `"exit"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.on`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:444
### on(event, listener)
**on**(`event`, `listener`): `this`
#### Parameters
• **event**: `"message"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.on`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:445
### on(event, listener)
**on**(`event`, `listener`): `this`
#### Parameters
• **event**: `"messageerror"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.on`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:446
### on(event, listener)
**on**(`event`, `listener`): `this`
#### Parameters
• **event**: `"online"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.on`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:447
### on(event, listener)
**on**(`event`, `listener`): `this`
#### Parameters
• **event**: `string` \| `symbol`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.on`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:448
***
## once()
### once(event, listener)
**once**(`event`, `listener`): `this`
Adds a **one-time**`listener` function for the event named `eventName`. The
next time `eventName` is triggered, this listener is removed and then invoked.
```js
server.once('connection', (stream) => {
console.log('Ah, we have our first user!');
});
```
Returns a reference to the `EventEmitter`, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The`emitter.prependOnceListener()` method can be used as an alternative to add the
event listener to the beginning of the listeners array.
```js
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
```
#### Parameters
• **event**: `"error"`
• **listener**
The callback function
#### Returns
`this`
#### Since
v0.3.0
#### Overrides
`EventEmitter.once`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:449
### once(event, listener)
**once**(`event`, `listener`): `this`
#### Parameters
• **event**: `"exit"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.once`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:450
### once(event, listener)
**once**(`event`, `listener`): `this`
#### Parameters
• **event**: `"message"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.once`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:451
### once(event, listener)
**once**(`event`, `listener`): `this`
#### Parameters
• **event**: `"messageerror"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.once`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:452
### once(event, listener)
**once**(`event`, `listener`): `this`
#### Parameters
• **event**: `"online"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.once`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:453
### once(event, listener)
**once**(`event`, `listener`): `this`
#### Parameters
• **event**: `string` \| `symbol`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.once`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:454
***
## postMessage()
**postMessage**(`value`, `transferList`?): `void`
Send a message to the worker that is received via `require('worker_threads').parentPort.on('message')`.
See `port.postMessage()` for more details.
### Parameters
• **value**: `any`
• **transferList?**: readonly `TransferListItem`[]
### Returns
`void`
### Since
v10.5.0
### Defined in
node\_modules/@types/node/worker\_threads.d.ts:401
***
## prependListener()
### prependListener(event, listener)
**prependListener**(`event`, `listener`): `this`
Adds the `listener` function to the _beginning_ of the listeners array for the
event named `eventName`. No checks are made to see if the `listener` has
already been added. Multiple calls passing the same combination of `eventName`and `listener` will result in the `listener` being added, and called, multiple
times.
```js
server.prependListener('connection', (stream) => {
console.log('someone connected!');
});
```
Returns a reference to the `EventEmitter`, so that calls can be chained.
#### Parameters
• **event**: `"error"`
• **listener**
The callback function
#### Returns
`this`
#### Since
v6.0.0
#### Overrides
`EventEmitter.prependListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:455
### prependListener(event, listener)
**prependListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"exit"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.prependListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:456
### prependListener(event, listener)
**prependListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"message"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.prependListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:457
### prependListener(event, listener)
**prependListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"messageerror"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.prependListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:458
### prependListener(event, listener)
**prependListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"online"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.prependListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:459
### prependListener(event, listener)
**prependListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `string` \| `symbol`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.prependListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:460
***
## prependOnceListener()
### prependOnceListener(event, listener)
**prependOnceListener**(`event`, `listener`): `this`
Adds a **one-time**`listener` function for the event named `eventName` to the_beginning_ of the listeners array. The next time `eventName` is triggered, this
listener is removed, and then invoked.
```js
server.prependOnceListener('connection', (stream) => {
console.log('Ah, we have our first user!');
});
```
Returns a reference to the `EventEmitter`, so that calls can be chained.
#### Parameters
• **event**: `"error"`
• **listener**
The callback function
#### Returns
`this`
#### Since
v6.0.0
#### Overrides
`EventEmitter.prependOnceListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:461
### prependOnceListener(event, listener)
**prependOnceListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"exit"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.prependOnceListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:462
### prependOnceListener(event, listener)
**prependOnceListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"message"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.prependOnceListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:463
### prependOnceListener(event, listener)
**prependOnceListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"messageerror"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.prependOnceListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:464
### prependOnceListener(event, listener)
**prependOnceListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"online"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.prependOnceListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:465
### prependOnceListener(event, listener)
**prependOnceListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `string` \| `symbol`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.prependOnceListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:466
***
## rawListeners()
**rawListeners**(`eventName`): `Function`[]
Returns a copy of the array of listeners for the event named `eventName`,
including any wrappers (such as those created by `.once()`).
```js
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));
// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];
// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();
// Logs "log once" to the console and removes the listener
logFnWrapper();
emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');
// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');
```
### Parameters
• **eventName**: `string` \| `symbol`
### Returns
`Function`[]
### Since
v9.4.0
### Inherited from
`EventEmitter.rawListeners`
### Defined in
node\_modules/@types/node/events.d.ts:542
***
## ref()
**ref**(): `void`
Opposite of `unref()`, calling `ref()` on a previously `unref()`ed worker does_not_ let the program exit if it's the only active handle left (the default
behavior). If the worker is `ref()`ed, calling `ref()` again has
no effect.
### Returns
`void`
### Since
v10.5.0
### Defined in
node\_modules/@types/node/worker\_threads.d.ts:408
***
## removeAllListeners()
**removeAllListeners**(`event`?): `this`
Removes all listeners, or those of the specified `eventName`.
It is bad practice to remove listeners added elsewhere in the code,
particularly when the `EventEmitter` instance was created by some other
component or module (e.g. sockets or file streams).
Returns a reference to the `EventEmitter`, so that calls can be chained.
### Parameters
• **event?**: `string` \| `symbol`
### Returns
`this`
### Since
v0.1.26
### Inherited from
`EventEmitter.removeAllListeners`
### Defined in
node\_modules/@types/node/events.d.ts:483
***
## removeListener()
### removeListener(event, listener)
**removeListener**(`event`, `listener`): `this`
Removes the specified `listener` from the listener array for the event named`eventName`.
```js
const callback = (stream) => {
console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);
```
`removeListener()` will remove, at most, one instance of a listener from the
listener array. If any single listener has been added multiple times to the
listener array for the specified `eventName`, then `removeListener()` must be
called multiple times to remove each instance.
Once an event is emitted, all listeners attached to it at the
time of emitting are called in order. This implies that any`removeListener()` or `removeAllListeners()` calls _after_ emitting and_before_ the last listener finishes execution will
not remove them from`emit()` in progress. Subsequent events behave as expected.
```js
const myEmitter = new MyEmitter();
const callbackA = () => {
console.log('A');
myEmitter.removeListener('event', callbackB);
};
const callbackB = () => {
console.log('B');
};
myEmitter.on('event', callbackA);
myEmitter.on('event', callbackB);
// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit('event');
// Prints:
// A
// B
// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit('event');
// Prints:
// A
```
Because listeners are managed using an internal array, calling this will
change the position indices of any listener registered _after_ the listener
being removed. This will not impact the order in which listeners are called,
but it means that any copies of the listener array as returned by
the `emitter.listeners()` method will need to be recreated.
When a single function has been added as a handler multiple times for a single
event (as in the example below), `removeListener()` will remove the most
recently added instance. In the example the `once('ping')`listener is removed:
```js
const ee = new EventEmitter();
function pong() {
console.log('pong');
}
ee.on('ping', pong);
ee.once('ping', pong);
ee.removeListener('ping', pong);
ee.emit('ping');
ee.emit('ping');
```
Returns a reference to the `EventEmitter`, so that calls can be chained.
#### Parameters
• **event**: `"error"`
• **listener**
#### Returns
`this`
#### Since
v0.1.26
#### Overrides
`EventEmitter.removeListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:467
### removeListener(event, listener)
**removeListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"exit"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.removeListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:468
### removeListener(event, listener)
**removeListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"message"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.removeListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:469
### removeListener(event, listener)
**removeListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"messageerror"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.removeListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:470
### removeListener(event, listener)
**removeListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `"online"`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.removeListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:471
### removeListener(event, listener)
**removeListener**(`event`, `listener`): `this`
#### Parameters
• **event**: `string` \| `symbol`
• **listener**
#### Returns
`this`
#### Overrides
`EventEmitter.removeListener`
#### Defined in
node\_modules/@types/node/worker\_threads.d.ts:472
***
## setMaxListeners()
**setMaxListeners**(`n`): `this`
By default `EventEmitter`s will print a warning if more than `10` listeners are
added for a particular event. This is a useful default that helps finding
memory leaks. The `emitter.setMaxListeners()` method allows the limit to be
modified for this specific `EventEmitter` instance. The value can be set to`Infinity` (or `0`) to indicate an unlimited number of listeners.
Returns a reference to the `EventEmitter`, so that calls can be chained.
### Parameters
• **n**: `number`
### Returns
`this`
### Since
v0.3.5
### Inherited from
`EventEmitter.setMaxListeners`
### Defined in
node\_modules/@types/node/events.d.ts:493
***
## terminate()
**terminate**(): `Promise`\<`number`\>
Stop all JavaScript execution in the worker thread as soon as possible.
Returns a Promise for the exit code that is fulfilled when the `'exit' event` is emitted.
### Returns
`Promise`\<`number`\>
### Since
v10.5.0
### Defined in
node\_modules/@types/node/worker\_threads.d.ts:420
***
## unref()
**unref**(): `void`
Calling `unref()` on a worker allows the thread to exit if this is the only
active handle in the event system. If the worker is already `unref()`ed calling`unref()` again has no effect.
### Returns
`void`
### Since
v10.5.0
### Defined in
node\_modules/@types/node/worker\_threads.d.ts:414
***
## getEventListeners()
`static` **getEventListeners**(`emitter`, `name`): `Function`[]
Returns a copy of the array of listeners for the event named `eventName`.
For `EventEmitter`s this behaves exactly the same as calling `.listeners` on
the emitter.
For `EventTarget`s this is the only way to get the event listeners for the
event target. This is useful for debugging and diagnostic purposes.
```js
const { getEventListeners, EventEmitter } = require('events');
{
const ee = new EventEmitter();
const listener = () => console.log('Events are fun');
ee.on('foo', listener);
getEventListeners(ee, 'foo'); // [listener]
}
{
const et = new EventTarget();
const listener = () => console.log('Events are fun');
et.addEventListener('foo', listener);
getEventListeners(et, 'foo'); // [listener]
}
```
### Parameters
• **emitter**: `EventEmitter` \| `DOMEventTarget`
• **name**: `string` \| `symbol`
### Returns
`Function`[]
### Since
v15.2.0, v14.17.0
### Inherited from
`EventEmitter.getEventListeners`
### Defined in
node\_modules/@types/node/events.d.ts:270
***
## ~~listenerCount()~~
`static` **listenerCount**(`emitter`, `eventName`): `number`
A class method that returns the number of listeners for the given `eventName`registered on the given `emitter`.
```js
const { EventEmitter, listenerCount } = require('events');
const myEmitter = new EventEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(listenerCount(myEmitter, 'event'));
// Prints: 2
```
### Parameters
• **emitter**: `EventEmitter`
The emitter to query
• **eventName**: `string` \| `symbol`
The event name
### Returns
`number`
### Since
v0.9.12
### Deprecated
Since v3.2.0 - Use `listenerCount` instead.
### Inherited from
`EventEmitter.listenerCount`
### Defined in
node\_modules/@types/node/events.d.ts:242
***
## on()
`static` **on**(`emitter`, `eventName`, `options`?): `AsyncIterableIterator`\<`any`, `any`, `any`\>
```js
const { on, EventEmitter } = require('events');
(async () => {
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo')) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
})();
```
Returns an `AsyncIterator` that iterates `eventName` events. It will throw
if the `EventEmitter` emits `'error'`. It removes all listeners when
exiting the loop. The `value` returned by each iteration is an array
composed of the emitted event arguments.
An `AbortSignal` can be used to cancel waiting on events:
```js
const { on, EventEmitter } = require('events');
const ac = new AbortController();
(async () => {
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo', { signal: ac.signal })) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
})();
process.nextTick(() => ac.abort());
```
### Parameters
• **emitter**: `EventEmitter`
• **eventName**: `string`
The name of the event being listened for
• **options?**: `StaticEventEmitterOptions`
### Returns
`AsyncIterableIterator`\<`any`, `any`, `any`\>
that iterates `eventName` events emitted by the `emitter`
### Since
v13.6.0, v12.16.0
### Inherited from
`EventEmitter.on`
### Defined in
node\_modules/@types/node/events.d.ts:221
***
## once()
### once(emitter, eventName, options)
`static` **once**(`emitter`, `eventName`, `options`?): `Promise`\<`any`[]\>
Creates a `Promise` that is fulfilled when the `EventEmitter` emits the given
event or that is rejected if the `EventEmitter` emits `'error'` while waiting.
The `Promise` will resolve with an array of all the arguments emitted to the
given event.
This method is intentionally generic and works with the web platform [EventTarget](https://dom.spec.whatwg.org/#interface-eventtarget) interface, which has no special`'error'` event
semantics and does not listen to the `'error'` event.
```js
const { once, EventEmitter } = require('events');
async function run() {
const ee = new EventEmitter();
process.nextTick(() => {
ee.emit('myevent', 42);
});
const [value] = await once(ee, 'myevent');
console.log(value);
const err = new Error('kaboom');
process.nextTick(() => {
ee.emit('error', err);
});
try {
await once(ee, 'myevent');
} catch (err) {
console.log('error happened', err);
}
}
run();
```
The special handling of the `'error'` event is only used when `events.once()`is used to wait for another event. If `events.once()` is used to wait for the
'`error'` event itself, then it is treated as any other kind of event without
special handling:
```js
const { EventEmitter, once } = require('events');
const ee = new EventEmitter();
once(ee, 'error')
.then(([err]) => console.log('ok', err.message))
.catch((err) => console.log('error', err.message));
ee.emit('error', new Error('boom'));
// Prints: ok boom
```
An `AbortSignal` can be used to cancel waiting for the event:
```js
const { EventEmitter, once } = require('events');
const ee = new EventEmitter();
const ac = new AbortController();
async function foo(emitter, event, signal) {
try {
await once(emitter, event, { signal });
console.log('event emitted!');
} catch (error) {
if (error.name === 'AbortError') {
console.error('Waiting for the event was canceled!');
} else {
console.error('There was an error', error.message);
}
}
}
foo(ee, 'foo', ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!
```
#### Parameters
• **emitter**: `NodeEventTarget`
• **eventName**: `string` \| `symbol`
• **options?**: `StaticEventEmitterOptions`
#### Returns
`Promise`\<`any`[]\>
#### Since
v11.13.0, v10.16.0
#### Inherited from
`EventEmitter.once`
#### Defined in
node\_modules/@types/node/events.d.ts:157
### once(emitter, eventName, options)
`static` **once**(`emitter`, `eventName`, `options`?): `Promise`\<`any`[]\>
#### Parameters
• **emitter**: `DOMEventTarget`
• **eventName**: `string`
• **options?**: `StaticEventEmitterOptions`
#### Returns
`Promise`\<`any`[]\>
#### Inherited from
`EventEmitter.once`
#### Defined in
node\_modules/@types/node/events.d.ts:162
***
## setMaxListeners()
`static` **setMaxListeners**(`n`?, ...`eventTargets`?): `void`
By default `EventEmitter`s will print a warning if more than `10` listeners are
added for a particular event. This is a useful default that helps finding
memory leaks. The `EventEmitter.setMaxListeners()` method allows the default limit to be
modified (if eventTargets is empty) or modify the limit specified in every `EventTarget` | `EventEmitter` passed as arguments.
The value can be set to`Infinity` (or `0`) to indicate an unlimited number of listeners.
```js
EventEmitter.setMaxListeners(20);
// Equivalent to
EventEmitter.defaultMaxListeners = 20;
const eventTarget = new EventTarget();
// Only way to increase limit for `EventTarget` instances
// as these doesn't expose its own `setMaxListeners` method
EventEmitter.setMaxListeners(20, eventTarget);
```
### Parameters
• **n?**: `number`
• ...**eventTargets?**: (`EventEmitter` \| `DOMEventTarget`)[]
### Returns
`void`
### Since
v15.3.0, v14.17.0
### Inherited from
`EventEmitter.setMaxListeners`
### Defined in
node\_modules/@types/node/events.d.ts:290