object-watch.js

/*
 * Object.watch shim
 *
 * 2015-12-26
 *
 * By Feifei Hang, http://feifeihang.info
 * Public Domain.
 * NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
 */
 
(function () {

  // Object.watch
  if (typeof Object.watch === 'undefined') {
    Object.watch = function watch(obj, prop, handler) {
      var oldVal = obj[prop];
      var newVal = oldVal;
      delete obj[prop];
      Object.defineProperty(obj, prop, {
        enumerable: true,
        configurable: true,
        get: function () { return newVal; },
        set: function (val) {
          oldVal = newVal;
          return newVal = handler.call(obj, prop, oldVal, val) || val;
        }
      });
    };
  }

  // Object.unwatch
  if (typeof Object.unwatch === 'undefined') {
    Object.unwatch = function unwatch (obj, prop) {
      var val = obj[prop];
      delete obj[prop];
      obj[prop] = val;
    };
  }

})();