function Dictionary(){var item,count;count=0;item={};this.add=function(name,value){if(!this.exists(name))count++;item[name]=value};this.item=function(name){return this.exists(name)?item[name]:null};this.exists=function(name){return name in item};this.remove=function(name){if(this.exists(name)&&delete item[name])count--};this.clear=function(){count=0;item={}};this.count=function(){return count};this.items=function(){var items=[];for(var name in item)items.push(name);return items}}