constructor

worker_threads.Worker.constructor

Not implemented in Bun

constructor Worker(

filename: string | URL,

@param filename

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.

Referenced types

interface URL

hash: string
host: string
hostname: string
href: string
readonly origin: string
password: string
pathname: string
port: string
protocol: string
search: string
readonly searchParams: URLSearchParams
username: string
toJSON(): string;

interface WorkerOptions

argv?: any[]
List of arguments which would be stringified and appended to process.argv in the worker. This is mostly similar to the workerData but the values will be available on the global process.argv as if they were passed as CLI options to the script.
env?: Dict<string> | typeof SHARE_ENV
eval?: boolean
execArgv?: string[]
name?: string
An optional name to be appended to the worker title for debugging/identification purposes, making the final title as [worker ${id}] ${name}.
resourceLimits?: ResourceLimits
stderr?: boolean
stdin?: boolean
stdout?: boolean
trackUnmanagedFds?: boolean
transferList?: Transferable[]
Additional data to send in the first worker message.
workerData?: any

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 streams may be redirected by the parent thread.
The import { isMainThread } from 'node:worker_threads' variable is set to false.
The import { parentPort } from 'node:worker_threads' 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). On Windows, unlike the main thread, a copy of the environment variables operates in a case-sensitive manner.
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 Workers is possible.

Like Web Workers and the node: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 theMessagePorts 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.

import assert from 'node:assert';
import {
  Worker, MessageChannel, MessagePort, isMainThread, parentPort,
} from 'node: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();
  });
}

readonly performance: WorkerPerformance
An object that can be used to query performance information from a worker instance. Similar to perf_hooks.performance.
readonly 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.
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.
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.
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.
readonly threadId: number
An integer identifier for the referenced thread. Inside the worker thread, it is available as import { threadId } from 'node:worker_threads'. This value is unique for each Worker instance inside a single process.
readonly threadName: null | string
A string identifier for the referenced thread or null if the thread is not running. Inside the worker thread, it is available as require('node:worker_threads').threadName.
[Symbol.asyncDispose](): Promise<void>;
Calls worker.terminate() when the dispose scope is exited.
async function example() { await using worker = new Worker('for (;;) {}', { eval: true }); // Worker is automatically terminate when the scope is exited. }
[events.captureRejectionSymbol](
error: Error,
event: string | symbol,
...args: any[]
): void;
The Symbol.for('nodejs.rejection') method is called in case a promise rejection happens when emitting an event and captureRejections is enabled on the emitter. It is possible to use events.captureRejectionSymbol in place of Symbol.for('nodejs.rejection').
import { EventEmitter, captureRejectionSymbol } from 'node:events'; class MyClass extends EventEmitter { constructor() { super({ captureRejections: true }); } [captureRejectionSymbol](err, event, ...args) { console.log('rejection happened for', event, 'with', err, ...args); this.destroy(err); } destroy(err) { // Tear the resource down here. } }
addListener<E extends keyof WorkerEventMap>(
eventName: E,
listener: (...args: WorkerEventMap[E]) => void
): this;
Alias for emitter.on(eventName, listener).
addListener(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
Alias for emitter.on(eventName, listener).
cpuUsage(
prev?: CpuUsage
): Promise<CpuUsage>;
This method returns a Promise that will resolve to an object identical to process.threadCpuUsage(), or reject with an ERR_WORKER_NOT_RUNNING error if the worker is no longer running. This methods allows the statistics to be observed from outside the actual thread.

emit<E extends keyof WorkerEventMap>(

eventName: E,

...args: WorkerEventMap[E]

): 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.

import { EventEmitter } from 'node: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

emit(

eventName: string | symbol,

...args: any[]

): 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.

import { EventEmitter } from 'node: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

eventNames(): string | symbol[];
Returns an array listing the events for which the emitter has registered listeners.
import { EventEmitter } from 'node: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) ]
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
A promise for a Readable Stream containing a V8 heap snapshot
getHeapStatistics(): Promise<HeapInfo>;
This method returns a Promise that will resolve to an object identical to v8.getHeapStatistics(), or reject with an ERR_WORKER_NOT_RUNNING error if the worker is no longer running. This methods allows the statistics to be observed from outside the actual thread.
getMaxListeners(): number;
Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to events.defaultMaxListeners.
listenerCount<E extends keyof WorkerEventMap>(
eventName: E,
listener?: (...args: WorkerEventMap[E]) => void
): number;
Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.
@param eventName
The name of the event being listened for
@param listener
The event handler function
listenerCount(
eventName: string | symbol,
listener?: (...args: any[]) => void
): number;
Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.
@param eventName
The name of the event being listened for
@param listener
The event handler function
listeners<E extends keyof WorkerEventMap>(
eventName: E
): (...args: WorkerEventMap[E]) => void[];
Returns a copy of the array of listeners for the event named eventName.
server.on('connection', (stream) => { console.log('someone connected!'); }); console.log(util.inspect(server.listeners('connection'))); // Prints: [ [Function] ]
listeners(
eventName: string | symbol
): (...args: any[]) => void[];
Returns a copy of the array of listeners for the event named eventName.
server.on('connection', (stream) => { console.log('someone connected!'); }); console.log(util.inspect(server.listeners('connection'))); // Prints: [ [Function] ]
off<E extends keyof WorkerEventMap>(
eventName: E,
listener: (...args: WorkerEventMap[E]) => void
): this;
Alias for emitter.removeListener().
off(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
Alias for emitter.removeListener().
on<E extends keyof WorkerEventMap>(
eventName: E,
listener: (...args: WorkerEventMap[E]) => void
): 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.
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.
import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.on('foo', () => console.log('a')); myEE.prependListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a
@param eventName
The name of the event.
@param listener
The callback function
on(
eventName: string | symbol,
listener: (...args: any[]) => void
): 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.
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.
import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.on('foo', () => console.log('a')); myEE.prependListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a
@param eventName
The name of the event.
@param listener
The callback function
once<E extends keyof WorkerEventMap>(
eventName: E,
listener: (...args: WorkerEventMap[E]) => void
): 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.
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.
import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.once('foo', () => console.log('a')); myEE.prependOnceListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a
@param eventName
The name of the event.
@param listener
The callback function
once(
eventName: string | symbol,
listener: (...args: any[]) => void
): 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.
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.
import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.once('foo', () => console.log('a')); myEE.prependOnceListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a
@param eventName
The name of the event.
@param listener
The callback function
postMessage(
value: any,
transferList?: readonly Transferable[]
): void;
Send a message to the worker that is received via require('node:worker_threads').parentPort.on('message'). See port.postMessage() for more details.
prependListener<E extends keyof WorkerEventMap>(
eventName: E,
listener: (...args: WorkerEventMap[E]) => void
): 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.
server.prependListener('connection', (stream) => { console.log('someone connected!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
@param eventName
The name of the event.
@param listener
The callback function
prependListener(
eventName: string | symbol,
listener: (...args: any[]) => void
): 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.
server.prependListener('connection', (stream) => { console.log('someone connected!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
@param eventName
The name of the event.
@param listener
The callback function
prependOnceListener<E extends keyof WorkerEventMap>(
eventName: E,
listener: (...args: WorkerEventMap[E]) => void
): 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.
server.prependOnceListener('connection', (stream) => { console.log('Ah, we have our first user!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
@param eventName
The name of the event.
@param listener
The callback function
prependOnceListener(
eventName: string | symbol,
listener: (...args: any[]) => void
): 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.
server.prependOnceListener('connection', (stream) => { console.log('Ah, we have our first user!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
@param eventName
The name of the event.
@param listener
The callback function

rawListeners<E extends keyof WorkerEventMap>(

eventName: E

): (...args: WorkerEventMap[E]) => void[];

Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).

import { EventEmitter } from 'node:events';
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');

rawListeners(

eventName: string | symbol

): (...args: any[]) => void[];

Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).

import { EventEmitter } from 'node:events';
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');

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.
removeAllListeners<E extends keyof WorkerEventMap>(
eventName?: E
): 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.
removeAllListeners(
eventName?: string | symbol
): 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.
removeListener<E extends keyof WorkerEventMap>(
eventName: E,
listener: (...args: WorkerEventMap[E]) => void
): this;
Removes the specified listener from the listener array for the event named eventName.
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.
import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} 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 indexes 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:
import { EventEmitter } from 'node:events'; 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.
removeListener(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
Removes the specified listener from the listener array for the event named eventName.
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.
import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} 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 indexes 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:
import { EventEmitter } from 'node:events'; 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.
setMaxListeners(
n: number
): this;
By default EventEmitters 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.
startCpuProfile(): Promise<CPUProfileHandle>;
Starting a CPU profile then return a Promise that fulfills with an error or an CPUProfileHandle object. This API supports await using syntax.
const { Worker } = require('node:worker_threads'); const worker = new Worker(` const { parentPort } = require('worker_threads'); parentPort.on('message', () => {}); `, { eval: true }); worker.on('online', async () => { const handle = await worker.startCpuProfile(); const profile = await handle.stop(); console.log(profile); worker.terminate(); });
await using example.
const { Worker } = require('node:worker_threads'); const w = new Worker(` const { parentPort } = require('node:worker_threads'); parentPort.on('message', () => {}); `, { eval: true }); w.on('online', async () => { // Stop profile automatically when return and profile will be discarded await using handle = await w.startCpuProfile(); });
startHeapProfile(): Promise<HeapProfileHandle>;
Starting a Heap profile then return a Promise that fulfills with an error or an HeapProfileHandle object. This API supports await using syntax.
const { Worker } = require('node:worker_threads'); const worker = new Worker(` const { parentPort } = require('worker_threads'); parentPort.on('message', () => {}); `, { eval: true }); worker.on('online', async () => { const handle = await worker.startHeapProfile(); const profile = await handle.stop(); console.log(profile); worker.terminate(); });
await using example.
const { Worker } = require('node:worker_threads'); const w = new Worker(` const { parentPort } = require('node:worker_threads'); parentPort.on('message', () => {}); `, { eval: true }); w.on('online', async () => { // Stop profile automatically when return and profile will be discarded await using handle = await w.startHeapProfile(); });
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.
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.