FetchEvent: handled property

Note: This feature is only available in Service Workers.

The handled property of the FetchEvent interface returns a promise indicating if the event has been handled by the fetch algorithm or not. This property allows executing code after the browser has consumed a response, and is usually used together with the waitUntil() method.

Value

A Promise that is pending while the event has not been handled, and fulfilled once it has.

Examples

js
addEventListener("fetch", (event) => {
  event.respondWith(
    (async function () {
      const response = await doCalculateAResponse(event.request);

      event.waitUntil(
        (async function () {
          await doSomeAsyncStuff(); // optional

          // Wait for the event to be consumed by the browser
          await event.handled;

          return doFinalStuff(); // Finalize AFTER the event has been consumed
        })(),
      );

      return response;
    })(),
  );
});

Specifications

Specification
Service Workers
# dom-fetchevent-handled

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
handled

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support
No support
No support

See also