userscripts/Abort Network Requests on Escape.user.js

// ==UserScript==
// @name        Abort Network Requests on Escape
// @namespace   blankie-scripts
// @match       http*://*/*
// @grant       none
// @version     1.0.0
// @author      blankie
// @description Aborts network requests invoked from XMLHttpRequest and fetch() when Escape is pressed
// @run-at      document-start
// @inject-into page
// ==/UserScript==

"use strict";

let activeXHRs = new Set();
let abortControllers = new Set();


unsafeWindow.XMLHttpRequest = new Proxy(unsafeWindow.XMLHttpRequest, {
    construct: function(target, args) {
        let xhr = new target(...args);
        xhr.addEventListener("loadstart", function() {
            activeXHRs.add(this);
        }, {passive: true});
        xhr.addEventListener("loadend", function() {
            activeXHRs.delete(this);
        }, {passive: true});
        return xhr;
    }
});

let originalFetch = unsafeWindow.fetch;
unsafeWindow.fetch = function(resource, options = undefined) {
    let abortController = new AbortController();
    options = options || {};

    let originalSignal = options.signal;
    if (originalSignal) {
        originalSignal.addEventListener("abort", function() {
            abortController.abort(originalSignal.reason);
        }, {passive: true});
    }
    options.signal = abortController.signal;

    abortControllers.add(abortController);

    return originalFetch.call(this, resource, options).finally(function() {
        abortControllers.delete(abortController);
    });
}


function abortAllRequests() {
    for (let activeXHR of activeXHRs) {
        activeXHR.abort();
    }
    activeXHRs.clear();

    let error = new DOMException("Network request cancelled by Abort Network Requests on Escape", "NetworkError");
    for (let abortController of abortControllers) {
        abortController.abort(error);
    }
    abortControllers.clear();
}

window.addEventListener("keydown", function(event) {
    if (event.key !== "Escape" || event.target !== document.body || event.altKey || event.ctrlKey || event.metaKey || event.shiftKey) {
        return;
    }
    abortAllRequests();
}, {passive: true});