Request: keepalive property

The keepalive read-only property of the Request interface contains the request's keepalive setting (true or false), which indicates whether the browser will keep the associated request alive if the page that initiated it is unloaded before the request is complete.

This enables a fetch() request to function as an alternative to Navigator.sendBeacon() when sending analytics at the end of a session, which has some advantages (you can use HTTP methods other than POST, customize request properties, and access the server response via the fetch Promise fulfillment). It is also available in service workers.

const options = {
  keepalive: true,
};

const myRequest = new Request("flowers.jpg", options);
let myKeepAlive = myRequest.keepalive; // true