function Hashtable() {     this._hash        = new Object();     this.add        = function(key,value){                         if(typeof(key)!="undefined"){                             if(this.contains(key)==false){                                 this._hash[key]=typeof(value)=="undefined"?null:value;                                 return true;                             } else {                                 return false;                             }                         } else {                             return false;                         }                     }     this.remove        = function(key){delete this._hash[key];}     this.count        = function(){var i=0;for(var k in this._hash){i++;} return i;}     this.items        = function(key){return this._hash[key];}     this.contains    = function(key){ return typeof(this._hash[key])!="undefined";}     this.clear        = function(){for(var k in this._hash){delete this._hash[k];}} }  var a = new Hashtable(); a.add("aa"); a.add("bb",2342); a.add("bb",2342); a.remove("aa"); alert(a.count()); alert(a.contains("bb")); alert(a.contains("aa")); alert(a.items("bb"));