ServiceWorkerContainer: startMessages() method

Secure contextAvailable in 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 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 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 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

startMessages()

Parameters

None.

Return value

undefined.

Examples

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

// …

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

navigator.serviceWorker.startMessages();

Specifications

Browser compatibility