<input type="text" placeholder="请输入邮箱" id="email">
<script>
email.onchange = function(){
var email = this.value;
var reg = /^([a-zA-Z]|[0-9])(\w|\-)+@[a-zA-Z0-9]+\.([a-zA-Z]{2,4})$/;
if(reg.test(email)){
alert("邮箱格式正确");
}else{
alert("邮箱格式不正确");
}
}
</script>
</html>
<input type="text" placeholder="请输入邮箱" id="email"