JavaScript推断E-mail地址是否合法

编写自己定义的JavaScript函数checkEmail(),在该函数中首先推断E-mail文本框是否为空,然后在应用正則表達式推断E-mail地址是否合法,假设不合法提示用户

<script type="text/javascript">
  		function checkEmail(){
  	  		var email = document.getElementById("email");
			if(email.value == null || email.value == ""){
				alert("请输入E-mail地址!");
				email.focus();
				return;
			}
			var regExp = /w+([-+.]w+)*@w+([-.]w+)*.w+([-.]w+)*/;
			if(!regExp.test(email.value)){
				alert("您输入的E-mail地址不对!");
				email.focus();
				return;
			}
  	  	}
  	</script><span style="white-space:pre">