属性监听器

在Proxy没有标准化之前，FF的Object.prototype.watch可是一个好东西。通过ecma262v5的特性描述符，我们可以实现此功能，这用于node.js最好不过了。

if ( ! Object.prototype.watch) {

    Object.defineProperty(Object.prototype, 'watch', {

        value: function (prop, handler) {

            var val = this[prop];

            var getter = function () {

                return val;

            };

            var setter = function (newVal) {

                var val = handler.call(this, prop, val, newVal);

            };

            if (delete (this[prop])) {

                Object.defineProperty(this, prop, {

                    get: getter,

                    set: setter,

                    configurable: true

                });

            }

        }

    });

}

/**

 * Object.unwatch() - Removes a watchpoint set with the watch method.

 * @param prop

 */

if ( ! Object.prototype.unwatch) {

    Object.defineProperty(Object.prototype, 'unwatch', {

        value: function (prop) {

            var val = this[prop];

            delete (this[prop]);

            this[prop] = val;

        }

    });

}

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