<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<script type="text/javascript">
var txt = 'DoYouKnowMe';
document.write(txt.substr(2,5)); //YouKn
document.write('<br />');
document.write(txt.substring(2,5)) //You
</script>
</head>
<body>
</body>
</html>
substr:（startindex,截取长度）,substring：（startindex,截取下标）