A simple class to manipulate key/value data, and execute a defined array callbacks.

DataModel.js

var DataModel = function () { "use strict";
  var data = {},
      callbacks = {
        'set' : [],
        'unset' : []
      },
      applyCallbacks = function (action, args) {
        var cb, len, i;
        if (callbacks[action] === undefined) return;
        len = callbacks[action].length;
        for (i=0; i < len; i++) {
          cb = callbacks[action][i];
          if (typeof cb === 'function') {
            cb.apply(undefined, args);
          }
        }
      };

  return {
    appendCallback : function (action, callback) {
      if (callbacks[action] !== undefined) {
        callbacks[action].push(callback);
      }
    },
    
    removeCallback : function (action, callback) {
      var cb, len, i;
      if (callbacks[action] === undefined) return;
      len = callbacks[action].length;
      for (i=0; i < len; i++) {
        cb = callbacks[action][i];
        if (cb === callback) {
          callbacks[action].splice(i, 1);
        }
      }
    },

    set : function (key, value) {
      data[key] = value;
      applyCallbacks('set', [key, value]);
    },

    unset : function (key) {
      if (data[key] !== undefined) {
        delete data[key];
        applyCallbacks('unset', [key]);
      }
    },

    get : function (key) {
      return data[key];
    },

    getAll : function () {
      return data;
    }
  };
};

example.js

var data = new DataModel()
  callbackA = function (key, value) {
    console.log('callbackA: ' + key + ' => ' + value);
  },
  callbackB = function (key, value) {
    console.log('callbackB: ' + key + ' => ' + value);
  },
  callbackC = function (key, value) {
    console.log('callbackC: ' + key + ' => ' + value);
  };

data.appendCallback('set', callbackA);
data.appendCallback('set', callbackB);
data.appendCallback('set', callbackC);
data.appendCallback('unset', function (key, value) {
  console.log('unset: ' + key + ' => ' + value);
});

data.set(12, "original text");
data.set(12, "new text");
data.removeCallback('set', cbB);
data.set(42, "forty two");
data.set(76, "seventy six");
data.set(123, "one hundred twenty three");
data.unset(76);
data.set("abc", "alphabeta")

console.log(data.getAll());
console.log(data.get(42));
console.log(data.get(234));
console.log(data.get("abc"));