js实现密码强度检验

<!DOCTYPE HTML>
<html lang="en">
<head>
 <meta charset="utf-8"/>
 <title>密码强度</title>
 <style type="text/css">
 #passStrength{height:6px;width:120px;border:1px solid #ccc;padding:2px;}
 .strengthLv1{background:red;height:6px;width:40px;}
 .strengthLv2{background:orange;height:6px;width:80px;}
 .strengthLv3{background:green;height:6px;width:120px;}
 </style>
</head>
<body>
 <input type="password" name="pass" id="pass" maxlength="16"/>
 <div class="pass-wrap">
 <em>密码强度：</em>
 <div id="passStrength"></div>
 </div>
</body>
</html>
<script type="text/javascript" src="js/passwordStrength.js"></script>
<script type="text/javascript">
new PasswordStrength('pass','passStrength');
</script>

function PasswordStrength(passwordID,strengthID){
 this.init(strengthID);
 var _this = this;
 document.getElementById(passwordID).onkeyup = function(){
 _this.checkStrength(this.value);
 }
};
PasswordStrength.prototype.init = function(strengthID){
 var id = document.getElementById(strengthID);
 var div = document.createElement('div');
 var strong = document.createElement('strong');
 this.oStrength = id.appendChild(div);
 this.oStrengthTxt = id.parentNode.appendChild(strong);
};
PasswordStrength.prototype.checkStrength = function (val){
 var aLvTxt = ['','低','中','高'];
 var lv = 0;
 if(val.match(/[a-z]/g)){lv++;}
 if(val.match(/[0-9]/g)){lv++;}
 if(val.match(/(.[^a-z0-9])/g)){lv++;}
 if(val.length < 6){lv=0;}
 if(lv > 3){lv=3;}
 this.oStrength.className = 'strengthLv' + lv;
 this.oStrengthTxt.innerHTML = aLvTxt[lv];
};