101 lines
2.5 KiB
Markdown
101 lines
2.5 KiB
Markdown
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---
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id: 587d7db1367417b2b2512b88
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title: Override Inherited Methods
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challengeType: 1
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forumTopicId: 301322
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dashedName: override-inherited-methods
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---
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# --description--
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In previous lessons, you learned that an object can inherit its behavior (methods) from another object by referencing its `prototype` object:
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```js
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ChildObject.prototype = Object.create(ParentObject.prototype);
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```
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Then the `ChildObject` received its own methods by chaining them onto its `prototype`:
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```js
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ChildObject.prototype.methodName = function() {...};
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```
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It's possible to override an inherited method. It's done the same way - by adding a method to `ChildObject.prototype` using the same method name as the one to override. Here's an example of `Bird` overriding the `eat()` method inherited from `Animal`:
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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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If you have an instance `let duck = new Bird();` and you call `duck.eat()`, this is how JavaScript looks for the method on the `prototype` chain of `duck`:
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1. `duck` => Is `eat()` defined here? No.
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2. `Bird` => Is `eat()` defined here? => Yes. Execute it and stop searching.
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3. `Animal` => `eat()` is also defined, but JavaScript stopped searching before reaching this level.
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4. Object => JavaScript stopped searching before reaching this level.
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# --instructions--
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Override the `fly()` method for `Penguin` so that it returns the string `Alas, this is a flightless bird.`
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# --hints--
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`penguin.fly()` should return the string `Alas, this is a flightless bird.`
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```js
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assert(penguin.fly() === 'Alas, this is a flightless bird.');
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```
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The `bird.fly()` method should return the string `I am flying!`
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```js
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assert(new Bird().fly() === 'I am flying!');
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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 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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# --solutions--
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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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