Hashtable = function() {
    this._hash = new Object();
    this.onPropertyChanged = function(added, updated, deleted) { }
    this.add = function(key, value) {
        if (typeof (key) != "undefined") {
            if (this.contains(key) == false) {
                this._hash[key] = typeof (value) == "undefined" ? null : value;
                this.onPropertyChanged([{ 'key': key, 'value': value}], [], []);
                return true;
            } else {
                this.setvalue(key,value);
            }
        } else {
            return false;
        }
    }

    this.remove = function(key) {
        var deleted = [{ 'key': key, 'value': this._hash[key]}];
        delete this._hash[key];
        this.onPropertyChanged([], [], deleted);
    }
    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(lazy) {
        var deleted = [];
        if (lazy == undefined || !lazy)
            deleted = this.allitems();

        for (var k in this._hash) {
            delete this._hash[k];
        }

        if (lazy == undefined || !lazy)
            this.onPropertyChanged([], [], deleted);
    }
    this.values = function() {
        var list = new Array();
        for (var k in this._hash)
            list[list.length] = this._hash[k];
        return list;
    }
    this.keys = function() {
        var list = new Array();
        for (var k in this._hash)
            list[list.length] = k;
        return list;
    }
    this.setvalue = function(key, value) { this._hash[key] = value; this.onPropertyChanged(this); }
    this.allitems = function() {
        var list = new Array();
        for (var k in this._hash) {
            list[list.length] = { key: k, value: this._hash[k] };
        }
        return list;
    }
}