<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>登录账号</title>
</head>
<body>
<h3>注册页面</h3>
<form action='a1.html' method='get' onsubmit='return checkForm'>
<table>
<tr>
<td>用户名：<input type='text' name='username' id='usernameId' onkeyup='checkName();'/></td>
<td><span id='usernameMsg'></span></td>
</tr>
</table>
</body>
<script type="text/javascript">
var usernameObj;
var usernameMsg;
window.onload=function(){
usernameObj=document.getElementById('usernameId');
usernameMsg=document.getElementById('usernameMsg');
}
function checkName(){
var x=usernameObj.value;
var regex=/^[a-zA-Z]\w{3,6}$/;
if(x == ''){
usernameMsg.innerHTML="用户名必须填写";
return false;
}
else if(!regex.test(x)){
usernameMsg.innerHTML="用户名已字母开始，长度4-7";
return false;
}
else{
usernameMsg.innerHTML="ok";
return true;
}
}
</script>
</html>
"用户名必须填写"和"用户名已字母开始，长度4-7"不在填写框后面显示
