JavaScript判断E-mail地址是否合法

<span style="font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">编写自定义的JavaScript函数checkEmail(),在该函数中首先判断E-mail文本框是否为空,然后在应用正则表达式判断E-mail地址是否合法,如果不合法提示用户</span>

<span style="font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);"></span><pre name="code" class="javascript"><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地址不正确!");
				email.focus();
				return;
			}
  	  	}
  	</script><span style="white-space:pre">	</span>