FetchEvent: handled property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨September 2022⁩.

Note: This feature is only available inService Workers.

Thehandled property of theFetchEvent 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 thewaitUntil() method.

Value

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

Examples

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;    })(),  );});