Simon game

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js"></script>
<div id="container">
  <div class="buttons">
    <div class="row">
      <button id="0" class="button button-red"></button>
      <button id="1" class="button button-green"></button>
    </div>
    <div class="row">
      <button id="2" class="button button-blue"></button>
      <button id="3" class="button button-yellow"></button>
    </div>
  </div>
  <button id="start">Start</button>
  <button id="stop">Stop</button>
</div>

CSS

.button {
  width: 150px;
  height: 150px;
}

.button-red {
  background-color: #B22222;
}

.button-green {
  background-color: green;
}

.button-blue {
  background-color: #000080;
}

.button-yellow {
  background-color: #e5e500;
}

JavaScript

var computer = [];
var check = [];

document.getElementById("0").addEventListener("click", clicked);
document.getElementById("1").addEventListener("click", clicked);
document.getElementById("2").addEventListener("click", clicked);
document.getElementById("3").addEventListener("click", clicked);

function clicked(e) {
 var colour = "";
 switch (Number(this.id)) {
    case 0:
        colour = "red";
        break;
    case 1:
        colour = "#7FFF00";
        break;
    case 2:
        colour = "blue";
        break;
    case 3:
        colour = "yellow";
        break;
}
 highlight(document.getElementById(this.id),colour);
 if(e.isTrusted){
 alert(computer);
 if(check.length > 0 && Number(this.id)===check[0]){
  check.shift(); 
 }
 if(check.length === 0 ){
  check = computer;
  play();
 }
 }
}

function highlight(obj, colour){
   var orig = obj.style.backgroundColor;
   obj.style.backgroundColor = colour;
   setTimeout(function(){
        obj.style.backgroundColor = orig;
   }, 1000);
}
function play (){
if(computer.length === 0){
next();
} else {
for(var i = 0; i < computer.length; i++){
timer(i);
}
setTimeout(function(){
next();
}, 2000*computer.length);
}
alert(computer);
}
 
function timer(i){
setTimeout(function(){
  document.getElementById(""+computer[i]).click();
}, 2000*i);
} 
function next(){
var random = Math.floor(Math.random() * 4);
computer.push(random);
check.push(random);
document.getElementById(""+random).click();
}

document.getElementById("start").addEventListener("click", play);