freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/object-oriented-programming/use-inheritance-so-you-dont-repeat-yourself.english.md

id, title, challengeType, forumTopicId

id	title	challengeType	forumTopicId
587d7db0367417b2b2512b83	Use Inheritance So You Don't Repeat Yourself	1	301334

Description

There's a principle in programming called Don't Repeat Yourself (DRY). The reason repeated code is a problem is because any change requires fixing code in multiple places. This usually means more work for programmers and more room for errors. Notice in the example below that the describe method is shared by Bird and Dog:

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);
  }
};

The describe method is repeated in two places. The code can be edited to follow the DRY principle by creating a supertype (or parent) called Animal:

function Animal() { };

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

Since Animal includes the describe method, you can remove it from Bird and Dog:

Bird.prototype = {
  constructor: Bird
};

Dog.prototype = {
  constructor: Dog
};

Instructions

The eat method is repeated in both Cat and Bear. Edit the code in the spirit of DRY by moving the eat method to the Animal supertype.

Tests

tests:
  - text: <code>Animal.prototype</code> should have the <code>eat</code> property.
    testString: assert(Animal.prototype.hasOwnProperty('eat'));
  - text: <code>Bear.prototype</code> should not have the <code>eat</code> property.
    testString: assert(!(Bear.prototype.hasOwnProperty('eat')));
  - text: <code>Cat.prototype</code> should not have the <code>eat</code> property.
    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");
  }
};