自己写的javascript map 函数, 用于统计字符出现次数

function Map(s) {    this.keys = new Array();    this.data = new Object();    this.put = function (key, value) {        if (this.data[key] == null) {            this.keys.push(key);            this.data[key] = value;        } else {            this.data[key] =this.data[key]+1;        }        return true;    };    this.get = function (key) {        return this.data[key]    }   for(var i=0; i<s.length;i++) {       this.put(s[i], 1);   }   return this.data;}