javascript使用正则表达式验证Email地址

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<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>测试：用Javascript正则表达式验证Email地址</title>
</head>
<body style="background:#fff;">
<p style="margin-bottom:20px;">
输入Email地址，点击测试，错误的地址将返回 false...正确的，显示成? 自己猜：
</p>
<input type="text" value="" id="mail"/>
<input type="button" value="测试" id="checkout" onclick="isValidMail(sText)" />
<script type="text/javascript">
 var sText = document.getElementById('mail').value;
 document.getElementById('mail').onblur = function sValue(){
  sText = this.value;
 }

 function isValidMail(sText) {
  var reMail = /^(?:[a-zA-Z0-9]+[_\-\+\.]?)*[a-zA-Z0-9]+@(?:([a-zA-Z0-9]+[_\-]?)*[a-zA-Z0-9]+\.)+([a-zA-Z]{2,})+$/;
  alert(reMail.test(sText))
 }
</script>
</body>
</html>