JavaScript 判断一个字符串中出现次数最多的字符；并统计此字符的个数

var str = “abcdefgaaaaaaddda”;
var obj = {};
var arr = [];
var letter;
for(var i = 0,len = str.length;i<len;i++){
   letter = str[i];
   if(!obj[letter]){
     obj[letter] = 1;
   }else{
     obj[letter]++;
   }
}
var max_key,max_num=0;
for(key in obj){
   if(max_num <obj[key]){
     max_num = obj[key];
     max_key = key;
   }
};    
document.write(“字母：”+max_key+”　次数：”+max_num);