2018-10-10 22:03:03 +00:00
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---
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id: 587d7db1367417b2b2512b88
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2021-03-15 03:20:39 +00:00
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title: 重写继承的方法
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2018-10-10 22:03:03 +00:00
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challengeType: 1
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2020-08-04 07:15:28 +00:00
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forumTopicId: 301322
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2021-01-13 02:31:00 +00:00
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dashedName: override-inherited-methods
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2018-10-10 22:03:03 +00:00
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---
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2020-12-16 07:37:30 +00:00
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# --description--
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2020-08-04 07:15:28 +00:00
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2021-03-15 03:20:39 +00:00
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在上一个挑战中,我们学习了一个对象可以通过引用另一个对象的 `prototype` 来继承其属性和行为(或方法):
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2020-08-04 07:15:28 +00:00
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```js
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ChildObject.prototype = Object.create(ParentObject.prototype);
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```
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2021-03-15 03:20:39 +00:00
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然后,`ChildObject` 将自己的方法链接到它的 `prototype`中:
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2020-08-04 07:15:28 +00:00
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```js
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ChildObject.prototype.methodName = function() {...};
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```
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2021-03-15 03:20:39 +00:00
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我们还可以重写继承的方法。 以同样的方式 - 通过使用一个与需要重写的方法相同的方法名,向`ChildObject.prototype` 中添加方法。 请看下面的举例:`Bird` 重写了从 `Animal` 继承来的 `eat()` 方法:
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2020-08-04 07:15:28 +00:00
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```js
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function Animal() { }
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Animal.prototype.eat = function() {
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return "nom nom nom";
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};
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function Bird() { }
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Bird.prototype = Object.create(Animal.prototype);
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Bird.prototype.eat = function() {
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return "peck peck peck";
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};
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```
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2021-03-15 03:20:39 +00:00
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如果你有一个实例:`let duck = new Bird();`,然后你调用了 `duck.eat()`,以下就是 JavaScript 在 `duck’s` 的 `prototype` 链上寻找方法的过程:
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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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1. `duck` => `eat()` 是定义在这里吗? 不是。
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2. `Bird` => `eat()` 是定义在这里吗? => 是的。 执行它并停止往上搜索。
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3. `Animal` => 这里也定义了 `eat()` 方法,但是 JavaScript 在到达这层原型链之前已停止了搜索。
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4. Object => JavaScript 在到达这层原型链之前也已经停止了搜索。
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2020-08-04 07:15:28 +00:00
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2020-12-16 07:37:30 +00:00
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# --instructions--
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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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重写 `Penguin` 的 `fly()` 方法,使其返回字符串 `Alas, this is a flightless bird.`
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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# --hints--
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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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`penguin.fly()` 方法应该返回字符串 `Alas, this is a flightless bird.`
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2018-10-10 22:03:03 +00:00
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```js
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assert(penguin.fly() === 'Alas, this is a flightless bird.');
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2018-10-10 22:03:03 +00:00
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```
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2021-03-15 03:20:39 +00:00
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The `bird.fly()`方法应该返回字符串 `I am flying!`
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2020-08-04 07:15:28 +00:00
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2018-10-10 22:03:03 +00:00
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```js
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assert(new Bird().fly() === 'I am flying!');
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2018-10-10 22:03:03 +00:00
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```
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2020-08-04 07:15:28 +00:00
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2021-01-13 02:31:00 +00:00
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# --seed--
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## --seed-contents--
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```js
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function Bird() { }
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Bird.prototype.fly = function() { return "I am flying!"; };
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function Penguin() { }
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Penguin.prototype = Object.create(Bird.prototype);
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Penguin.prototype.constructor = Penguin;
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// Only change code below this line
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// Only change code above this line
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let penguin = new Penguin();
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console.log(penguin.fly());
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```
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2020-12-16 07:37:30 +00:00
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# --solutions--
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2021-01-13 02:31:00 +00:00
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```js
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function Bird() { }
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Bird.prototype.fly = function() { return "I am flying!"; };
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function Penguin() { }
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Penguin.prototype = Object.create(Bird.prototype);
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Penguin.prototype.constructor = Penguin;
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Penguin.prototype.fly = () => 'Alas, this is a flightless bird.';
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let penguin = new Penguin();
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console.log(penguin.fly());
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```
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