js 求字符串某个字母出现的最大次数

<!DOCTYPE HTML>
<html>
<head>
   <meta http-equiv="content-type" content="text/html; charset=utf-8">

   <title>Max_val</title>

</head>
<body>
   <div class="">

</div>

</body>
<script type="text/javascript" charset="utf-8">
//将字符串的字符保存在一个hash table中，key是字符，value是这个字符出现的次数
var str = "abcdefgadddaaaaaaaaab";
var obj = {};
for (var i = 0, l = str.length; i < l; i++)
{
var key = str[i];
if (!obj[key])
   {
　 obj[key] = 1;
　　}
    else
    {
　　 obj[key]++;
　　}
}
/*遍历这个hash table，获取value最大的key和value*/
var max = 0;
var max_key = "";

for (index in obj)
{
    if (max < obj[index])
      {
        max = obj[index];
        max_key = index;
    }
}

alert("max_count:"+max+" max_key:"+max_key);

</script>

</html>