set data structure built on top of js object

set.js

var Set = function() {
  this._items = {};
};

Set.prototype = {
  values: function() { 
    return Object.keys(this._items);
  },

  insert: function(val) {
    if (this._items[val]) return false;
    this._items[val] = true;
    return true;
  },

  remove: function(val) { delete(this._items[val]); }
};