Web/API/ServiceWorkerContainer/startMessages

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 ServiceWorkerContainer.onmessage. In this you don't need startMessages().

Syntax

serviceWorkerContainer.startMessages();

Parameters

None.

Return value

undefined.

Examples

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

// ...

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

navigator.serviceWorker.startMessages();

Specifications

Specification	Status	Comment
Service WorkersThe definition of 'ServiceWorkerContainer: startMessages()' in that specification.	Working Draft	Initial definition.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`startMessages`	Chrome Full support 74	Edge Full support ≤79	Firefox Full support 64	IE No support No	Opera Full support 62	Safari Full support Yes	WebView Android Full support 74	Chrome Android Full support 74	Firefox Android Full support 64	Opera Android Full support 50	Safari iOS Full support Yes	Samsung Internet Android Full support 11.0

Legend

Full support: Full support
No support: No support

ServiceWorkerContainer.startMessages() by Mozilla Contributors is licensed under CC-BY-SA 2.5.