原生JS实现圣旨卷轴展开效果

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>诏书</title>
 <style type="text/css">
 * {
  margin: 0;
  padding: 0;
 }
 #animate {
  margin: 40px auto;
  width: 495px;
  height: 150px;
  position: relative;
  overflow: hidden;
 }
 #back {
  width: 495px;
  height: 150px;
  position: absolute;
  left: 0;
  top: 10px;
  background: url(http://cdn.attach.qdfuns.com/notes/pics/201703/04/191654mcfqzdfrxann5551.png) no-repeat;
 }
 #left {
  position: absolute;
  left: 0;
 }
 #right {
  position: absolute;
  left: 16px;
 }
 #mark {
  position: absolute;
  left: 44px;
 }
 </style>
</head>
<body>
<div id="animate">
 <div id="back"><img src="http://cdn.attach.qdfuns.com/notes/pics/201703/04/191214ug6h47d81jyfy6vh.png"/></div>
 <div id="left"><img src="http://cdn.attach.qdfuns.com/notes/pics/201703/04/191236gldigxmxg2zlh9s7.png"/></div>
 <div id="right"><img src="http://cdn.attach.qdfuns.com/notes/pics/201703/04/191244uhavf49l1zw440cv.png"/></div>
 <div id="mark"><img src="http://cdn.attach.qdfuns.com/notes/pics/201703/04/191254kfbz2tjupc1jigbb.png"/></div>
</div>
</body>
<script>
 var animate=document.getElementById("animate");
 var right = document.getElementById("right");
 var mark = document.getElementById("mark");
 var timer = setInterval(function () {
 var right1=getComputedStyle(right).left;
 var mark1=getComputedStyle(mark).left;
 if(parseFloat(right1)>=447){
  right1=447+"px";
  clearInterval(timer);
 }
 right.style.left=(parseFloat(right1)+10)+"px";
 mark.style.left=(parseFloat(mark1)+10)+"px";
 }, 100)
</script>
</html>