kahoot-hotkeys.user.js

// ==UserScript==
// @name         Kahoot hotkeys
// @namespace    mvolfik.github.io
// @version      0.2
// @description  take over the world!
// @author       mvolfik
// @match        https://kahoot.it/v2/*
// ==/UserScript==

(function() {
    document.onkeypress=function(e){
        console.log(e.keyCode);
        switch (e.keyCode) {
            case 52:
                document.querySelectorAll("button[data-functional-selector~=answer-0]")[0].click();
                break;
            case 53:
                document.querySelectorAll("button[data-functional-selector~=answer-1]")[0].click();
                break;
            case 49:
                document.querySelectorAll("button[data-functional-selector~=answer-2]")[0].click();
                break;
            case 50:
                document.querySelectorAll("button[data-functional-selector~=answer-3]")[0].click();
                break;
        }
    }
})();