检测输入密码长度

<script language=javascript>   
//CharMode函数   
//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>