js 实现 map

  function getMap() {//初始化map_,给map_对象增加方法，使map_像Map             var map_ = new Object();             map_.put = function(key, value) {                 map_[key+'_'] = value;             };             map_.get = function(key) {                 return map_[key+'_'];             };             map_.remove = function(key) {                 delete map_[key+'_'];             };             map_.keyset = function() {                 var ret = "";                 for(var p in map_) {                     if(typeof p == 'string' && p.substring(p.length-1) == "_") {                         ret += ",";                         ret += p.substring(0,p.length-1);                     }                 }                 if(ret == "") {                     return ret.split(",");                 } else {                     return ret.substring(1).split(",");                 }             };             return map_;    }