js Hashtable

Hashtable = function() {
 this.items = new Array();
 this.itemsCount = 0;
 this.add = function(key, value) {
  if (!this.containsKey(key)) {
   this.items[key] = value;
   this.itemsCount++;
  }
 }
 this.get = function(key) {
  if (this.containsKey(key))
   return this.items[key];
  else
   return null;
 }

 this.keys = function() {
  var keys = new Array();
  for (var i in this.items) {
   if (this.items[i] != null)
    keys.push(i);
  }
  return keys;
 }

 this.values = function() {
  var values = new Array();
  for (var i in this.items) {
   if (this.items[i] != null)
    values.push(this.items[i]);
  }
  return values;
 }
 this.remove = function(key) {
  if (this.containsKey(key)) {
   delete this.items[key];
   this.itemsCount--;
  }
 }
 this.containsKey = function(key) {
  return typeof(this.items[key]) != "undefined";

 }
 this.containsValue = function containsValue(value) {
  for (var item in this.items) {
   if (this.items[item] == value)
    return true;
   break;
  }
  return false;
 }

 this.contains = function(keyOrValue) {
  return this.containsKey(keyOrValue) || this.containsValue(keyOrValue);
 }
 this.clear = function() {
  this.items = new Array();
  itemsCount = 0;
 }
 this.size = function() {
  var size = 0;
  for (var i in this.items) {
   if (this.items[i] != null)
    size++;
  }
  return size;
 }
 this.isEmpty = function() {
  return this.size() == 0;
 }

 this.toString = function() {
  var result = '';
  for (var i in this.items) {
   if (this.items[i] != null)
    result += '{' + i + '},{' + this.items[i] + '}\n';
  }
  return result;
 }

};