http://www.reddit.com/r/javascript/comments/24lci1/manipulating_javascript_objects_of_key_value/

MasterStore.js

function MasterStore() {
  this.datastore = {};
}

MasterStore.prototype.has = function(key, value){
  if (value == null) return this.datastore.hasOwnProperty(key);
  if (Array.isArray(value)) {
    for (var i = 0; i < value.length; i++) {
      if (this.datastore[key].indexOf(value[i]) < 0) {
        return false;
      }
    }
    return true;
  }
  return this.datastore[key].indexOf(value) >= 0;
};

MasterStore.prototype.add = function (key, value) {
  if (value == null) return this;
  var valueIsArray = Array.isArray(value);
  if (this.datastore.hasOwnProperty(key)) {
    // if value is an array and the datastore[key] is also an array
    if (valueIsArray) {
      // concatenate the value array to the datastore[key] array
      this.datastore[key] = this.datastore[key].concat(value);
    } else if (this.datastore[key].indexOf(value) >= 0) {
      //if present then do nothing 
    } else {
      // otherwise push value onto the datastore[key] array
      this.datastore[key].push(value);
    }
  } else {
    this.datastore[key] = valueIsArray ? value : [value];
  }
  return this;
}

MasterStore.prototype.remove = function (key, value) {
  if (value == null) {
    // if no value present then remove the whole array from the datastore
    delete this.datastore[key];
    return this;
  }
  var valueIsArray = Array.isArray(value);
  if (this.datastore.hasOwnProperty(key)) {
    if (Array.isArray(value)) {
      // should we keep splicing the array or just create a new one
      if (value.length < 20) {
        // if we don't have a lot of values to remove, just splice
        for (var i = 0; i < value.length; i++) {
          var index = this.datastore[key].indexOf(value[i]); 
          if (index >= 0) this.datastore[key].splice(index, 1);
        }
      } else {
        // otherwise it's probably faster to just create a new array
        var store = this.datastore[key], tmp = [];
        for (var i = 0; i < store.length; i++) {
          var index = value.indexOf(store[i]);
          if (index < 0) {
            // if datastore[key][i] isn't in the value array
            // push it into our new array
            tmp.push(store[i]);
          }
        }
        this.datastore[key] = tmp;
      }
    } else {
      var index = this.datastore[key].indexOf(value);  
      if (index >= 0) this.datastore[key].splice(index, 1);
    }
  }
  return this;
}

masterStore.js

var a = new MasterStore;
a.add('days', 'monday');
console.log(a.datastore.days);  //>> ['monday']

// You can also chain because add() and remove() return this
console.log(a.add('days', 'tuesday').datastore.days);    //>> ['monday', 'tuesday']
a.add('days', 'wednesday').remove('days', 'tuesday');
console.log(a.datastore.days);   //>> ['monday', 'wednesday']

// You can add entire arrays at a time
a.add('months', ['january', 'february', 'march']);
a.add('months', ['april', 'may', 'june']);
console.log(a.datastore.months);    //>> ['january', 'february', 'march', 'april', 'may', 'june']

// You can remove individual values from the datastore[key] array
a.remove('months', 'february');
console.log(a.datastore.months);    //>> ['january', 'march', 'april', 'may', 'june']

// You can remove multiple values from the datastore[key] array
a.remove('months', ['january', 'april', 'june']);
console.log(a.datastore.months);    //>> ['march', 'may']

// You can also entirely remove the datastore[key] array
// (this is mostly for convince as you can do: "delete datastore[key];" instead)
a.remove('months');
console.log(a.datastore.months);    //>> undefined