JavaScript实现简易单数字随机抽奖特效

<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>简易的单数字随机抽奖，抽取随机数的js特效代码</title>
</head>
<body>
<div id="num"></div>
<input value="start" id="start" type="button" />
<input value="stop" id="stop" type="button" />
<script>
var num = document.getElementById("num");
var start = document.getElementById("start");
var _stop = document.getElementById("stop");
var intv = null;
start.onclick = function(){
 
 if(intv==undefined){
 
 intv = setInterval(function(){num.innerHTML = Math.floor(Math.random()*10);},50);
 
 }
 
}
_stop.onclick = function(){
 
 clearInterval(intv);
 
 intv=null;
 
}
</script>
</body>
</html>