示例代码：
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
</head>
<body>
Email：<input type="text" id="email">
<input type="submit" value ="提交" onclick="onEmail()"/>
</body>
<script language="javascript">
function onEmail(){
//邮箱校验
var email = document.getElementById("email").value;
if(email == null || email == undefined || email == ""){
alert("Email不能为空");
document.getElementById("email").focus();//重新获取焦点
return false;
}
//邮箱格式的判断
if(!email.match(/^([a-zA-Z0-9_-])+@([a-zA-Z0-9_-])+((\.[a-zA-Z0-9_-]{2,3}){1,2})$/)) {
alert("Email格式错误!");
document.getElementById("email").focus();//重新获取焦点
return false;
}else{
alert("Email格式通过!");
}
}
</script>
</html>