JS写的Hashtable

function Hashtable() {
    this._hash = new Object();
    //add()
    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;
        }
    }
    //remove()
    this.remove = function(key){delete this._hash[key];}
    //count
    this.count = function(){var i=0;for(var k in this._hash){i++;} return i;}
    //items
    this.items = function(key){return this._hash[key];}
    //contains
    this.contains = function(key){ return typeof(this._hash[key])!="undefined";}
    //clear
    this.clear = function(){for(var k in this._hash){delete this._hash[k];}}
}