Whatsapp Web Show Hide contacts

try to take over the world!
Mint 2017.03.25.. Lásd a legutóbbi verzió
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// ==UserScript==
// @name         Whatsapp Web Show Hide contacts
// @namespace    http://tampermonkey.net/
// @version      1.0
// @description  try to take over the world!
// @author       RHueara
// @match        https://web.whatsapp.com/
// @grant        none
// ==/UserScript==

(function() {
    'use strict';
    var hidden = false;
    var defaultbkg = 'lightgrey';
    var prevName = '';
    var sheet = window.document.styleSheets[0];
    sheet.insertRule('@keyframes btnanimate { 0% {background-color: red; left:70px;} 25%{left:55px;} 50%{left:85px;} 75% {left:65px;} 100% {background-color: white;left:70px;} }', sheet.cssRules.length);

    window.addEventListener('load', () => {
     checkScreenLoaded();
     document.addEventListener("keydown", function(e) {
         var keyCode = e.keyCode;
         if(keyCode==118) {
             toggleShowHide();
         }
     }, false);
    });
    function checkScreenLoaded() {
        setTimeout(function(){
            if (document.getElementsByClassName('intro-image')[0] != null) {
                addButton('Hide / F7', toggleShowHide);
            } else {
                checkScreenLoaded();
            }
        }, 20);
    }
    function addButton(text, onclick, cssObj) {
        cssObj = cssObj || {position: 'absolute', top: '15px', left:'70px', 'z-index': 3, 'font-weight':'bold', border:'black solid', 'border-radius':'10px',
                            padding:'4px', 'animation-duration': '200ms', 'background-color': defaultbkg, 'min-width': '75px'};
        let button = document.createElement('button'), btnStyle = button.style;
        document.body.appendChild(button);
        button.innerHTML = text;
        button.onclick = onclick;
        button.classList = ['show-hide-btn'];
        document.getElementsByClassName('show-hide-btn')[0].addEventListener('webkitAnimationEnd', function(){
            this.style.webkitAnimationName = '';
        }, false);
        button.onmouseover = function(){document.getElementsByClassName('show-hide-btn')[0].style["background-color"] = 'salmon';};
        button.onmouseout = function(){document.getElementsByClassName('show-hide-btn')[0].style["background-color"] = defaultbkg;};
        Object.keys(cssObj).forEach(key => btnStyle[key] = cssObj[key]);
        return button;
    }

    function toggleShowHide() {
        var btn = document.getElementsByClassName('show-hide-btn')[0];
        btn.style.webkitAnimationName = 'btnanimate';
        var panel = document.getElementsByClassName('chatlist-panel-body')[0];
        if (hidden) {
            panel.setAttribute('style', 'display:block');
            defaultbkg = 'lightgrey';
            btn.innerHTML = 'Hide / F7';
            try {
                document.getElementsByTagName('h2')[0].getElementsByTagName('span')[0].innerHTML = prevName;
                document.getElementsByClassName('pane-chat-header')[0].getElementsByTagName('img')[0].setAttribute('style', 'display:block;');
            } catch(e) {
            }
            prevName = '';
        } else {
            panel.setAttribute('style', 'display:none');
            defaultbkg = 'red';
            btn.innerHTML = 'Show / F7';
            try {
                prevName = document.getElementsByTagName('h2')[0].getElementsByTagName('span')[0].innerHTML;
                document.getElementsByTagName('h2')[0].getElementsByTagName('span')[0].innerHTML = 'Not-suspicious and Random Person';
                document.getElementsByClassName('pane-chat-header')[0].getElementsByTagName('img')[0].setAttribute('style', 'display:none;');
            } catch(e) {
            }
        }
        hidden = !hidden;
    }
})();