郵箱驗證-JS正則表達式

<input type="text" placeholder="請輸入郵箱" 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("郵箱格式正確");
        }else{
            alert("郵箱格式不正確");
        }
    }
</script>
</html>