js创建map集合

function createMap(){ 
                     //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_;
}