JavaScript实现局部页面打印功能

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<script type="text/javascript">  
  function doPrint() {  
    bdhtml=window.document.body.innerHTML;  
    sprnstr="<!--startprint-->";  
    eprnstr="<!--endprint-->";  
    prnhtml=bdhtml.substr(bdhtml.indexOf(sprnstr)+17);  
    prnhtml=prnhtml.substring(0,prnhtml.indexOf(eprnstr));  
    window.document.body.innerHTML=prnhtml; 
    window.print();  
}  
</script>
</head>
 
<body>
<p>1</p>
<p>2</p>
<!--startprint--><!--注意要加上html里star和end的这两个标记，之前没加，一直没效果，谁叫咱们菜呢~-->
<h1>打印标题</h1>
<p>打印内容~~</p>
<!--endprint-->
<button type="button" onclick="doPrint()">打印</button>
<p>1</p>
<p>2</p>
</body>
</html>