How do I cancel an HTTP fetch() request?

TL/DR:

fetch now supports a signal parameter as of 20 September 2017, but not all browsers seem support this at the moment.

2020 UPDATE: Most major browsers (Edge, Firefox, Chrome, Safari, Opera, and a few others) support the feature, which has become part of the DOM living standard. (as of 5 March 2020)

This is a change we will be seeing very soon though, and so you should be able to cancel a request by using an AbortControllers AbortSignal.

Long Version

How to:

The way it works is this:

Step 1: You create an AbortController (For now I just used this)

const controller = new AbortController()

Step 2: You get the AbortControllers signal like this:

const signal = controller.signal

Step 3: You pass the signal to fetch like so:

fetch(urlToFetch, {    method: 'get',    signal: signal, // <------ This is our AbortSignal})

Step 4: Just abort whenever you need to:

controller.abort();

Here's an example of how it would work (works on Firefox 57+):

<script>    // Create an instance.    const controller = new AbortController()    const signal = controller.signal    /*    // Register a listenr.    signal.addEventListener("abort", () => {        console.log("aborted!")    })    */    function beginFetching() {        console.log('Now fetching');        var urlToFetch = "https://httpbin.org/delay/3";        fetch(urlToFetch, {                method: 'get',                signal: signal,            })            .then(function(response) {                console.log(`Fetch complete. (Not aborted)`);            }).catch(function(err) {                console.error(` Err: ${err}`);            });    }    function abortFetching() {        console.log('Now aborting');        // Abort.        controller.abort()    }</script><h1>Example of fetch abort</h1><hr><button onclick="beginFetching();">    Begin</button><button onclick="abortFetching();">    Abort</button>

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