setInterval(fn,1000)//正确
setInterval(fn(),1000)//错误

window.onload = function() {
 var timer = null;
 var num = 0;
 var i = 0; 
 var arr=['red','#FF9D0C','#DBFF0D','#3BFF0D','#0DFFA2','#0DE8FF','#0D52FF','#210DFF','#930DFF','#FF0DB4']
 var start = document.getElementById('start');
 var stop = document.getElementById('stop');
 var prizeDraw = document.getElementById('prizeDraw');
 start.onclick = function() {
 clearInterval(timer);
 timer = setInterval(function(){ 
 num = Math.floor(Math.random()*100+1);
 prizeDraw.style.backgroundColor = arr[i];
 i++;
 if (i==9) {
 i = 0;
 };
 prizeDraw.innerHTML = num;
 },100);
 }
 stop.onclick = function() {
 clearInterval(timer);
 }
}

#prizeDraw {
 width: 100px;
 height: 100px;
 background: rgba(255,68,253,0.5);
 font-size: 30px;
 text-align: center;
 line-height: 100px;
 }

<div id="prizeDraw"></div>
 <input type="button" value="开始" id="start">
 <input type="button" value="暂停" id="stop">