The message event is used in a page controlled by a service worker to receive messages from the service worker.

This event is not cancelable and does not bubble.

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

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

onmessage = (event) => {};

A MessageEvent. Inherits from Event.

This interface also inherits properties from its parent, Event.

MessageEvent.data 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).

In this example the service worker get the client's ID from a fetch event and then sends it a message using Client.postMessage:

// service-worker.js
async function messageClient(clientId) {
  const client = await clients.get(clientId);
  client.postMessage("Hi client!");
}

addEventListener("fetch", (event) => {
  messageClient(event.clientId);
  event.respondWith(() => {
    // …
  });
});

The client can receive the message by listening to the message event:

// main.js
navigator.serviceWorker.addEventListener("message", (message) => {
  console.log(message);
});

Alternatively, the client can receive the message with the onmessage event handler:

// main.js
navigator.serviceWorker.onmessage = (message) => {
  console.log(message);
};

• Using Service Workers
• Service workers basic code example
• Is ServiceWorker ready?
• Using web workers