81 lines
1.8 KiB
Markdown
81 lines
1.8 KiB
Markdown
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---
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id: 587d7dad367417b2b2512b78
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title: 使用構造函數創建對象
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challengeType: 1
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forumTopicId: 18233
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dashedName: use-a-constructor-to-create-objects
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---
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# --description--
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在上一個挑戰中，我們用所學到的知識創建了一個 `Bird` 構造函數：
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```js
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function Bird() {
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this.name = "Albert";
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this.color = "blue";
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this.numLegs = 2;
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}
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let blueBird = new Bird();
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```
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**注意：** 構造函數內的 `this` 總是指被創建的對象。
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注意：通過構造函數創建對象的時候要使用 `new` 操作符。 因爲只有這樣，JavaScript 才知道要給 `Bird` 這個構造函數創建一個新的實例：`blueBird`。 如果不使用 `new` 操作符來新建對象，那麼構造函數裏面的 `this` 就無法指向新創建的這個對象實例，從而產生不可預見的錯誤。 現在 `blueBird` 這個實例就繼承了`Bird` 構造函數的所有屬性，如下：
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```js
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blueBird.name;
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blueBird.color;
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blueBird.numLegs;
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```
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由構造函數創建的實例也和其他對象一樣，它的屬性可以被訪問和修改：
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```js
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blueBird.name = 'Elvira';
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blueBird.name;
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```
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# --instructions--
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使用上一個挑戰中的 `Dog` 構造函數創建一個 `Dog` 的新實例，並把它賦值給變量 `hound`。
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# --hints--
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`hound` 應該是通過 `Dog` 構造函數來創建的。
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```js
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assert(hound instanceof Dog);
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```
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你的代碼中應該使用 `new` 操作符來創建 `Dog` 構造函數的新實例。
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```js
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assert(code.match(/new/g));
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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 Dog() {
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this.name = "Rupert";
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this.color = "brown";
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this.numLegs = 4;
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}
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// Only change code below this line
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```
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# --solutions--
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```js
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function Dog() {
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this.name = "Rupert";
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this.color = "brown";
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this.numLegs = 4;
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}
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const hound = new Dog();
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```
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