Note: This feature is only available in Service Workers.

The ExtendableMessageEvent interface of the Service Worker API represents the event object of a message event fired on a service worker (when a message is received on the ServiceWorkerGlobalScope from another context) — extends the lifetime of such events.

This interface inherits from the ExtendableEvent interface.

Event ExtendableEvent ExtendableMessageEvent



Creates a new ExtendableMessageEvent object instance.

Instance properties

Inherits properties from its parent, ExtendableEvent.

ExtendableMessageEvent.data Read only

Returns the event's data. It can be any data type. If dispatched in messageerror event, the property will be null.

ExtendableMessageEvent.origin Read only

Returns the origin of the Client that sent the message.

ExtendableMessageEvent.lastEventId Read only

Represents, in server-sent events, the last event ID of the event source.

ExtendableMessageEvent.source Read only

Returns a reference to the Client object that sent the message.

ExtendableMessageEvent.ports Read only

Returns the array containing the MessagePort objects representing the ports of the associated message channel.

Instance methods

Inherits methods from its parent, ExtendableEvent.


In the below example a page gets a handle to the ServiceWorker object via ServiceWorkerRegistration.active, and then calls its postMessage() function.

// in the page being controlled
if (navigator.serviceWorker) {

  navigator.serviceWorker.addEventListener("message", (event) => {
    // event is a MessageEvent object
    console.log(`The service worker sent me a message: ${event.data}`);

  navigator.serviceWorker.ready.then((registration) => {
    registration.active.postMessage("Hi service worker");

The service worker can receive the message by listening to the message event:

// in the service worker
addEventListener("message", (event) => {
  // event is an ExtendableMessageEvent object
  console.log(`The client sent me a message: ${event.data}`);

  event.source.postMessage("Hi client");


Service Workers
# extendablemessageevent-interface

Browser compatibility

BCD tables only load in the browser

See also