这个ie8的兼容是个问题，ie8 的innerHTML有问题啊，添加两个附件吧
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<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<title>多用户留言系统-</title>
<meta name="description" content="">
<meta name="keywords" content="">
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<script type="text/javascript">
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var can = document.getElementById('can');
var pro = can.innerHTML.substring(0,can.innerHTML.length-1);
console.log(pro);
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cxt.arc(100,100,100,0,Math.PI*2*90/100,false);
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html5.js
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