ServiceWorkerContainer: startMessages() method

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since April 2018.

Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

Note: This feature is available in Web Workers.

The startMessages() method of the ServiceWorkerContainer interface explicitly starts the flow of messages being dispatched from a service worker to pages under its control (e.g. sent via Client.postMessage()). This can be used to react to sent messages earlier, even before that page's content has finished loading.

Explanation

By default, all messages sent from a page's controlling service worker to the page (using Client.postMessage()) are queued while the page is loading, and get dispatched once the page's HTML document has been loaded and parsed (i.e. after the DOMContentLoaded event fires). It's possible to start dispatching these messages earlier by calling ServiceWorkerContainer.startMessages(), for example if you've invoked a message handler using EventTarget.addEventListener() before the page has finished loading, but want to start processing the messages right away.

Note: The messages start being sent automatically when setting the handler directly using onmessage. In this you don't need startMessages().

Syntax

js
startMessages()

Parameters

None.

Return value

undefined.

Examples

js
if ("serviceWorker" in navigator) {
  navigator.serviceWorker.register("/sw.js").then(() => {
    console.log("Service Worker Registered");
  });
}

// …

navigator.serviceWorker.addEventListener("message", (e) => {
  // …
});

navigator.serviceWorker.startMessages();

Specifications

Specification
Service Workers
# navigator-service-worker-startMessages

Browser compatibility

Report problems with this compatibility data on GitHub
desktopmobile
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
startMessages

Legend

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Full support
Full support
No support
No support