JS实现带数字显示的环形进度条

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<link>
<meta name="page-view-size" content="640*530">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<style>
 .wapper{
  position:absolute;
  left:100px;
  top:100px;
  box-sizing:border-box;
 }
 .text{
  position:absolute;
  left:30px;
  top:40px;
  font-family:"Microsoft YaHei";
  font-weight:bold;
  color:indianred;
 }
 .rect{
  position:absolute;
  width:50px;
  height:100px;
  overflow:hidden;
 }
 .right{
  left:50px;
 }
 .circle{
  position:absolute;
  width:100px;
  height:100px;
  border-radius:50%;
  box-sizing:border-box;
  border:5px solid indianred;
 }
 .circle_right{
  left:-50px;
  clip:rect(0px 50px 100px 0px);
  animation:roll 5s linear 0s 1 forwards;
 }
 .circle_left{
  clip:rect(0px 100px 100px 50px);
  animation:roll 5s linear 5s 1 forwards;
 }
 @keyframes roll{
  0%{transform:rotate(0deg)}
  100%{ transform:rotate(180deg)}
 }
</style>
<body leftmargin="0" topmargin="0">
<div class="wapper">
 <div class="rect right"><div class="circle circle_right"></div></div>
 <div class="rect left"><div class="circle circle_left"></div></div>
 <div class="text"><span id="num">1</span><span>%</span></div>
</div>
</body>
<script type="text/javascript">
 window.onload=function(){
  var $num=document.getElementById('num');
  (function(){
   var i=1,timer;
   add();
   function add(){
    var timer=setTimeout(function(){
     add();
    },100);
    $num.innerHTML=i;
    i<100?i++:clearTimeout(timer)
   }
  })();
 }
</script>
</html>