2021-05-05 10:13:49 -07:00
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---
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id: 587d7db1367417b2b2512b86
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title: 重置一個繼承的構造函數屬性
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challengeType: 1
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forumTopicId: 301324
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dashedName: reset-an-inherited-constructor-property
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---
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# --description--
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當一個對象從另一個對象那裏繼承了其 `prototype` 時,那它也繼承了父類的 constructor 屬性。
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請看下面的舉例:
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```js
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function Bird() { }
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Bird.prototype = Object.create(Animal.prototype);
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let duck = new Bird();
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duck.constructor
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```
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2021-06-21 19:13:43 +05:30
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但是 `duck` 和其他所有 `Bird` 的實例都應該表明它們是由 `Bird` 創建的,而不是由 `Animal` 創建的。 爲此,你可以手動將 `Bird` 的構造函數屬性設置爲 `Bird` 對象:
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2021-05-05 10:13:49 -07:00
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```js
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Bird.prototype.constructor = Bird;
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duck.constructor
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```
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# --instructions--
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修改你的代碼,使得 `duck.constructor` 和 `beagle.constructor` 返回各自的構造函數。
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# --hints--
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`Bird.prototype` 應該是 `Animal` 的一個實例。
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```js
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assert(Animal.prototype.isPrototypeOf(Bird.prototype));
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```
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`duck.constructor` 應該返回 `Bird`。
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```js
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assert(duck.constructor === Bird);
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```
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`Dog.prototype` 應該是 `Animal` 的一個實例。
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```js
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assert(Animal.prototype.isPrototypeOf(Dog.prototype));
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```
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`beagle.constructor` 應該返回 `Dog`。
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```js
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assert(beagle.constructor === Dog);
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```
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# --seed--
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## --seed-contents--
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```js
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function Animal() { }
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function Bird() { }
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function Dog() { }
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Bird.prototype = Object.create(Animal.prototype);
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Dog.prototype = Object.create(Animal.prototype);
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// Only change code below this line
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let duck = new Bird();
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let beagle = new Dog();
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```
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# --solutions--
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```js
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function Animal() { }
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function Bird() { }
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function Dog() { }
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Bird.prototype = Object.create(Animal.prototype);
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Dog.prototype = Object.create(Animal.prototype);
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Dog.prototype.constructor = Dog;
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Bird.prototype.constructor = Bird;
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let duck = new Bird();
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let beagle = new Dog();
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```
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