object-watch.js

/*
 * object.watch polyfill
 *
 * 2012-04-03
 *
 * By Eli Grey, http://eligrey.com
 * Public Domain.
 * NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
 */

// object.watch
if (!Object.prototype.watch) {
	Object.defineProperty(Object.prototype, 'watch', {
		enumerable: false,
		configurable: true,
		writable: false,
		value: function (prop, handler) {
			'use strict';
			var oldval = this[prop],
				newval = oldval,
				getter = function () {
					return newval;
				},
				setter = function (val) {
					oldval = newval;
					return newval = handler.call(this, prop, oldval, val);
				};

			if (delete this[prop]) { // can't watch constants
				Object.defineProperty(this, prop, {
					get: getter,
					set: setter,
					enumerable: true,
					configurable: true
				});
			}
		}
	});
}

// object.unwatch
if (!Object.prototype.unwatch) {
	Object.defineProperty(Object.prototype, 'unwatch', {
		enumerable: false,
		configurable: true,
		writable: false,
		value: function (prop) {
			'use strict';
			var val = this[prop];
			delete this[prop]; // remove accessors
			this[prop] = val;
		}
	});
}