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

---
id: 587d7db0367417b2b2512b83
title: Use Inheritance So You Don't Repeat Yourself
challengeType: 1
forumTopicId: 301334
dashedName: use-inheritance-so-you-dont-repeat-yourself
---

# --description--

There's a principle in programming called <dfn>Don't Repeat Yourself (DRY)</dfn>. 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`:

```js
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`:

```js
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`:

```js
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`.

# --hints--

`Animal.prototype` should have the `eat` property.

```js
assert(Animal.prototype.hasOwnProperty('eat'));
```

`Bear.prototype` should not have the `eat` property.

```js
assert(!Bear.prototype.hasOwnProperty('eat'));
```

`Cat.prototype` should not have the `eat` property.

```js
assert(!Cat.prototype.hasOwnProperty('eat'));
```

# --seed--

## --seed-contents--

```js
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,

};
```

# --solutions--

```js
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");
  }
};
```