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()). Can be used to avoid race conditions created when a service worker tries to post a message to a page before that page has actually finished loading an ServiceWorkerContainer.onmessage handler to process them..

Explanation

Messages sent from the service worker to a document would get stored in its client message queue, and would previously start getting dispatched when one of two things occur:

• When ServiceWorkerContainer.onmessage is set up to handle the messages.
• When the page content finishes loading (e.g. on DOMContentLoaded).

There is a possible race condition here — if the page content has finished loading before the onmessage handler has been set, the messages could be lost because there is nothing to handle it.

startMessages() has been implemented to mitigate this race condition. If you want message sending to start before the page content has loaded, you can explicitly call this method.

Syntax

ServiceWorkerContainer.startMessages();

Parameters

None.

Return value

Void.

Examples

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

...

navigator.serviceWorker.startMessages();

navigator.serviceWorker.onmessage() {
  ...
};

Specifications

Browser compatibilityUpdate compatibility data on GitHub