JS–比想象中简单

<span style="font-family:KaiTi_GB2312;font-size:18px;"><form id="registerForm" οnsubmit=" checkForm();">
</form></span>

<span style="font-family:KaiTi_GB2312;font-size:18px;"><script>        //校验表单内容是否为空
	function checkForm(){
		//校验用户名
		//获得用户名文本框的值
		var username=document.getElementById("username").value;
		if(username == null || username == ''){
			alert("用户名不能为空！");
			return false;
		}
		
		//校验密码
		//获得密码框的值
		var password = document.getElementById("password").value;
		if(password == null || password ==''){
			alert("密码不能为空！");
			return false;
		}
	}	
</script></span>

<span style="font-family:KaiTi_GB2312;font-size:18px;">		//校验邮箱
		var email = document.getElementById("email").value;
		var filter  = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
		if(filter.test(email)){
			return true;
		}else{
			alert("邮箱格式不正确！");
			return false;
		}</span>