object.watch polyfill in ES5

object-watch.js

/*
 * object.watch polyfill
 *
 * 2012-04-03
 *
 * By Eli Grey, http://eligrey.com
 * Modified by Joseph Dalrymple, http://swivel.in
 * 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) {
			var curVal = this[prop];

			if (delete this[prop]) { // can't watch constants
				Object.defineProperty(this, prop, {
					get: function () {
						return curVal;
					},
					set: function (val) {
						return curVal = handler.call(this, prop, curVal, val);
					},
					enumerable: true,
					configurable: true
				});
			}
		}
	});
}

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