js实现密码强度

<!doctype html>
<html>

<head>
<meta charset="utf-8">
<title>js密码强度</title>
<style type="text/css">
.pw_letter{ margin-top:5px; font-size: 12px; }
.pw_letter label{float: left; margin-right:10px; cursor: default; font-size: 12px; line-height: 16px;;}
.pw_letter span{ float: left; display:inline-block; width:30px; height:16px; line-height:16px; text-align:center; 
color:#FFF; background-color:#ccc; border-left: 1px solid #FFF;}
.pw_letter span.pw_strength_color{ background-color:green;}

</style>
</head>

<body>

<input id="password" type="password" name="password" placeholder="密码" onKeyUp="setPasswordStrength(this.value.trim())">
<div class="pw_letter"><label>安全程度</label> <span class="strength">弱</span> <span class="strength">中</span> 

<span class="strength">强</span> </div>

<script type="text/javascript">
/*
*密码安全程度
*return 1 ：全部为字母或者数字,或者密码长度小于6
*return 2 : 字母数字组成，或者字母特殊字符，或者数字和特殊字符
*return 3 : 字母和数字和特殊字符
*/
String.prototype.passwordStrength=function(){
if(this.length>0 && this.length<=6) return 1;
var n1 = (this.search(/[a-zA-Z]/) != -1) ? 1 : 0,
n2 = (this.search(/[0-9]/) != -1) ? 1 : 0,
n3 =(this.search(/[\~\`\!\@\#\$\%\^\&\*\(\)\_\+\-\=\[\]|{\}\;\'\:\"\,\.\/\<\>\?]{1,}/) != -1) ? 1 : 0;
return n1+n2+n3;
}

String.prototype.trim = String.prototype.trim || function(){
return this.replace(/^\s+|\s+$/g,"");
}

function setPasswordStrength(pwd){
var strength_span = document.getElementsByClassName("strength");
for(var i=0; i<strength_span.length; i++){
strength_span.item(i).className="strength";
}
for(var i=0; i<pwd.passwordStrength(); i++){
document.getElementsByClassName("strength").item(i).className="strength pw_strength_color";
}
}

</script>
</body>

</html>