Give notifications when A Dark Room's Gather button should be clicked again

aDarkRoomNotifierForTamperMonkey.js

// ==UserScript==
// @name         A Dark Room notifier
// @namespace    http://adarkroom.doublespeakgames.com/
// @version      0.1
// @description  try to take over the world!
// @author       You
// @match        http://adarkroom.doublespeakgames.com/
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    // request notification permission on page load
    document.addEventListener('DOMContentLoaded', function () {
        if (!Notification) {
            alert('Desktop notifications not available in your browser. Try Chromium.'); 
            return;
        }
        if (Notification.permission !== "granted")
            Notification.requestPermission();
    });

    // give a little notice when the buttons can be clicked again
    addClassNameListener("gatherButton", function(){ checkButton("gatherButton","G"); });
    addClassNameListener("trapsButton", function(){ checkButton("trapsButton", "T"); });
    console.log("A Dark Room - listener started");
})();

function checkButton(elemId, letter) {
    console.log("checkButton("+elemId+"," + letter + ")");
    if (!stringContains(document.getElementById(elemId).className, "disabled")){
        notifyMe(letter);
    }
}

function stringContains(haystack, needle){
    return haystack.indexOf(needle) !== -1;
}

//http://stackoverflow.com/questions/10612024/event-trigger-on-class-change
function addClassNameListener(elemId, callback) {
    var elem = document.getElementById(elemId);
    var lastClassName = elem.className;
    window.setInterval( function() {
        var className = elem.className;
        if (className !== lastClassName) {
            callback();
            lastClassName = className;
        }
    },100);
}


//http://stackoverflow.com/questions/2271156/chrome-desktop-notification-example
function notifyMe(letter) {
    if (Notification.permission !== "granted")
        Notification.requestPermission();
    else {
        var notification = new Notification('A Dark Room', {
            icon: 'https://raw.githubusercontent.com/doublespeakgames/adarkroom/master/favicon.ico',
            body: "Hey there! You've been notified!" + letter,
        });
        notification.onclick = function () {
            //nothing..
        };
    }
}



////MEUK
function checkButtonOld(elemId, letter){
    console.log("checkButton("+elemId+"," + letter + ")");
    if (stringContains(document.getElementById(elemId).className, "disabled")){
        //button disabled? remove notify-letter
        if (document.title.startsWith(letter)){
            document.title = document.title.substring(1);
        }
    } else {
        //if notify-letter is already added, don't add again
        if (!document.title.startsWith(letter)){
            document.title = letter + document.title;
        }
    }
}