用于判断用户注册时，密码强度的JS代码。

<script language=javascript>  
//CharMode函数
//source:www.web2bar.cn  
//测试某个字符是属于哪一类.  
function CharMode(iN){  
if (iN>=48 && iN <=57) //数字  
return 1;  
if (iN>=65 && iN <=90) //大写字母  
return 2;  
if (iN>=97 && iN <=122) //小写  
return 4;  
else  
return 8; //特殊字符  
}  
//bitTotal函数  
//计算出当前密码当中一共有多少种模式  
function bitTotal(num){  
modes=0;  
for (i=0;i<4;i++){  
if (num & 1) modes++;  
num>>>=1;  
}  
return modes;  
}  
//checkStrong函数  
//返回密码的强度级别  
function checkStrong(sPW){  
if (sPW.length<=4)  
return 0; //密码太短  
Modes=0;  
for (i=0;i<sPW.length;i++){  
//测试每一个字符的类别并统计一共有多少种模式.  
Modes|=CharMode(sPW.charCodeAt(i));  
}  
return bitTotal(Modes);  
}  
//pwStrength函数  
//当用户放开键盘或密码输入框失去焦点时,根据不同的级别显示不同的颜色  
function pwStrength(pwd){  
O_color="#eeeeee";  
L_color="#FF0000";  
M_color="#FF9900";  
H_color="#33CC00";  
if (pwd==null||pwd==''){  
Lcolor=Mcolor=Hcolor=O_color;  
}  
else{  
S_level=checkStrong(pwd);  
switch(S_level) {  
case 0:  
Lcolor=Mcolor=Hcolor=O_color;  
case 1:  
Lcolor=L_color;  
Mcolor=Hcolor=O_color;  
break;  
case 2:  
Lcolor=Mcolor=M_color;  
Hcolor=O_color;  
break;  
default:  
Lcolor=Mcolor=Hcolor=H_color;  
}  
}
document.getElementById("strength_L").style.background=Lcolor;  
document.getElementById("strength_M").style.background=Mcolor;  
document.getElementById("strength_H").style.background=Hcolor;  
return;  
}  
</script>  
<form name=form1 action="" >  
输入密码:
<input type=password size=10 onKeyUp=pwStrength(this.value) 
onBlur=pwStrength(this.value)>  
<br>密码强度:  
<table width="217" border="1" cellspacing="0" cellpadding="1" bordercolor="#cccccc"
height="23" style='display:inline'>  
<tr align="center" bgcolor="#eeeeee">  
<td width="33%" id="strength_L">弱</td>  
<td width="33%" id="strength_M">中</td>  
<td width="33%" id="strength_H">强</td>  
</tr>  
</table>
</form>