freeCodeCamp/use-inheritance-so-you-dont-repeat-yourself.md at dec409a4bd667e4979305cc1e86e0702bbc2c707

Oliver Eyton-Williams dec409a4bd fix: s/localeTitle/title/g

2020-10-06 23:10:08 +05:30

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id, challengeType, forumTopicId, title

id	challengeType	forumTopicId	title
587d7db0367417b2b2512b83	1	301334	使用继承避免重复

Description

有一条原则叫做：Don't Repeat Yourself，常以缩写形式DRY出现，意思是“不要自己重复”。编写重复代码会产生的问题是：任何改变都需要去多个地方修复所有重复的代码。这通常意味着我们需要做更多的工作，会产生更高的出错率。请观察下面的示例，Bird和Dog共享describe方法：

Bird.prototype = {
  constructor: Bird,
  describe: function() {
    console.log("My name is " + this.name);
  }
};

Dog.prototype = {
  constructor: Dog,
  describe: function() {
    console.log("My name is " + this.name);
  }
};

我们可以看到describe方法在两个地方重复定义了。根据以上所说的DRY原则，我们可以通过创建一个Animal 超类（或者父类）来重写这段代码：

function Animal() { };

Animal.prototype = {
  constructor: Animal, 
  describe: function() {
    console.log("My name is " + this.name);
  }
};

Animal构造函数中定义了describe方法，可将Bird和Dog这两个构造函数的方法删除掉：

Bird.prototype = {
  constructor: Bird
};

Dog.prototype = {
  constructor: Dog
};

Instructions

Cat和Bear重复定义了eat方法。本着DRY的原则，通过将eat方法移动到Animal 超类中来重写你的代码。

Tests

tests:
  - text: <code>Animal.prototype</code>应该有<code>eat</code>属性。
    testString: assert(Animal.prototype.hasOwnProperty('eat'));
  - text: <code>Bear.prototype</code>不应该有<code>eat</code>属性。
    testString: assert(!(Bear.prototype.hasOwnProperty('eat')));
  - text: <code>Cat.prototype</code>不应该有<code>eat</code>属性。
    testString: assert(!(Cat.prototype.hasOwnProperty('eat')));

Challenge Seed

function Cat(name) {
  this.name = name;
}

Cat.prototype = {
  constructor: Cat,
  eat: function() {
    console.log("nom nom nom");
  }
};

function Bear(name) {
  this.name = name;
}

Bear.prototype = {
  constructor: Bear,
  eat: function() {
    console.log("nom nom nom");
  }
};

function Animal() { }

Animal.prototype = {
  constructor: Animal,

};

Solution

function Cat(name) {
  this.name = name;
}

Cat.prototype = {
  constructor: Cat
};

function Bear(name) {
  this.name = name;
}

Bear.prototype = {
  constructor: Bear
};

function Animal() { }

Animal.prototype = {
  constructor: Animal,
  eat: function() {
    console.log("nom nom nom");
  }
};

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