Enforcing new 模式

			// 构造函数
			function Waffle() {
				this.tastes = "yummy";
			}

			// 反例
			// 忘记使用 `new`
			var good_morning = Waffle();
			console.log(typeof good_morning); // "undefined"
			console.log(window.tastes); // "yummy"   此时构造函数Waffle中的this指代window


			//更改为使用new关键字
			var good_morning = new Waffle();
			console.log(typeof good_morning); // "object"
			console.log(good_morning.tastes); // "yummy"


			// 强制使用new
			function Waffle() {
				if (!(this instanceof Waffle)) {
					return new Waffle();
				}

				this.tastes = "yummy";
			}

			var good_morning = new Waffle();
			var good_evening = Waffle();

			console.log(typeof good_morning); // "object"
			console.log(good_morning.tastes); // "yummy"
			console.log(typeof good_evening); // "object"
			console.log(good_evening.tastes); // "yummy"