if (!Object.prototype.watch) {
    Object.defineProperty(Object.prototype, "watch", {
        enumerable: false,
        configurable: true,
        writable: false,
        value: function (prop, handler) {
            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
                });
            }
        }
    });
}

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;
        }
    });
}