Worker: message event

Note: This feature is available in Web Workers, except for Service Workers.

The message event is fired on a Worker object when the worker's parent receives a message from its worker (i.e. when the worker sends a message using DedicatedWorkerGlobalScope.postMessage()).

This event is not cancellable and does not bubble.


Use the event name in methods like addEventListener(), or set an event handler property.

addEventListener("message", (event) => {});

onmessage = (event) => {};

Event type

Event properties

This interface also inherits properties from its parent, Event. Read only

The data sent by the message emitter.

MessageEvent.origin Read only

A string representing the origin of the message emitter.

MessageEvent.lastEventId Read only

A string representing a unique ID for the event.

MessageEvent.source Read only

A MessageEventSource (which can be a WindowProxy, MessagePort, or ServiceWorker object) representing the message emitter.

MessageEvent.ports Read only

An array of MessagePort objects representing the ports associated with the channel the message is being sent through (where appropriate, e.g. in channel messaging or when sending a message to a shared worker).


This code creates a new worker and listens to messages from it using addEventListener():

const worker = new Worker("static/scripts/worker.js");

worker.addEventListener("message", (event) => {
  console.log(`Received message from worker: ${}`);

Alternatively, it could listen using the onmessage event handler property:

const worker = new Worker("static/scripts/worker.js");

worker.onmessage = (event) => {
  console.log(`Received message from worker: ${}`);

The worker posts messages using self.postMessage():

// static/scripts/worker.js

self.postMessage("I'm alive!");


HTML Standard
# event-message

Browser compatibility

BCD tables only load in the browser

See also