js获取字符串长度

<SCRIPT LANGUAGE="JavaScript">
<!--
function Len(str)
{
var i,sum;
sum=0;
for(i=0;i<str.length;i++)
{
if ((str.charCodeAt(i)>=0) && (str.charCodeAt(i)<=255))
sum=sum+1;
else
sum=sum+2;
}
return sum;
}
function checkPasswordLen(){
passwd1   = document.getElementById('passwd').value;
if(Len(passwd1)<6)
{
alert("密码长度不能小于6！");
document.getElementById('passwd').focus();
}

}