JS表單驗證 郵箱

<form action="" method="post">
    <input type="text" name="email" id="email" onblur="emai(this.value)" value="" onfocus="f()" />
    <span id="tisi">郵箱長度最多20位   </span>
    <span id="emailnull">不能爲空！    </span>
    <span id="emailro">請輸入正確的郵箱格式！</span>
    <span id="emailyes">正確！</span>
</form>

<script type="text/javascript">
           
            var email=document.getElementById('email');
            var emailnull=document.getElementById('emailnull');
            var emailro=document.getElementById('emailro');
            var emailyes=document.getElementById('emailyes');
             var tisi=document.getElementById('tisi');
            //alert(email.value)
            function f(){
            	 emailro.style.display='none';
                emailyes.style.display='none';
                emailnull.style.display='none';
                tisi.style.display='block';
            	
            }
            function emai(e){
            	 tisi.style.display='none';
                var ereg=/^(\w+)@(\w+)\.([a-zA-Z]){2,5}$/;
                var reg=ereg.test(e);
               
                if(e==""){
                     emailnull.style.display="block";
                }else if(reg){
                	
                     emailyes.style.display="block";
                }else{
                	
                     emailro.style.display="block";
                }
            }
        </script>