<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>网站首页</title>
<style>
</style>
</head>
<body>
<form action="save.php" method="post" onSubmit="return check()">
账号：<input type="text" id="account" name="account">
<input type="submit" value="提交">
</form>
</body>
</html>
<script>
function $(id){
return document.getElementById(id);
}
String.prototype.trim =function(){
return this.replace(/^\s+|\s+$/g,‘‘);
}
function check(){
var aa=$(‘account‘);
var ac=aa.value.trim();
aa.value=ac;
var p=/^[a-z]{6,12}$/i;
if(!p.test(ac)){
alert(‘账号必须为6-12位英文字母‘);
aa.focus();
return false;
}
return true;
}
</script>
原文：http://www.cnblogs.com/lsr111/p/4449944.html