freeCodeCamp/curriculum/challenges/chinese/02-javascript-algorithms-and-data-structures/object-oriented-programming/add-methods-after-inheritance.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
587d7db1367417b2b2512b87	Add Methods After Inheritance	1	301315	add-methods-after-inheritance

--description--

A constructor function that inherits its prototype object from a supertype constructor function can still have its own methods in addition to inherited methods.

For example, Bird is a constructor that inherits its prototype from Animal:

function Animal() { }
Animal.prototype.eat = function() {
  console.log("nom nom nom");
};
function Bird() { }
Bird.prototype = Object.create(Animal.prototype);
Bird.prototype.constructor = Bird;

In addition to what is inherited from Animal, you want to add behavior that is unique to Bird objects. Here, Bird will get a fly() function. Functions are added to Bird's prototype the same way as any constructor function:

Bird.prototype.fly = function() {
  console.log("I'm flying!");
};

Now instances of Bird will have both eat() and fly() methods:

let duck = new Bird();
duck.eat(); // prints "nom nom nom"
duck.fly(); // prints "I'm flying!"

--instructions--

Add all necessary code so the Dog object inherits from Animal and the Dog's prototype constructor is set to Dog. Then add a bark() method to the Dog object so that beagle can both eat() and bark(). The bark() method should print "Woof!" to the console.

--hints--

Animal should not respond to the bark() method.

assert(typeof Animal.prototype.bark == 'undefined');

Dog should inherit the eat() method from Animal.

assert(typeof Dog.prototype.eat == 'function');

Dog should have the bark() method as an own property.

assert(Dog.prototype.hasOwnProperty('bark'));

beagle should be an instanceof Animal.

assert(beagle instanceof Animal);

The constructor for beagle should be set to Dog.

assert(beagle.constructor === Dog);

beagle.eat() should log "nom nom nom"

console.log = function (msg) {
  throw msg;
};
assert.throws(() => beagle.eat(), 'nom nom nom');

beagle.bark() should log "Woof!"

console.log = function (msg) {
  throw msg;
};
assert.throws(() => beagle.bark(), 'Woof!');

--seed--

--seed-contents--

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

function Dog() { }

// Only change code below this line




// Only change code above this line

let beagle = new Dog();

--solutions--

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

function Dog() { }
Dog.prototype = Object.create(Animal.prototype);
Dog.prototype.constructor = Dog;
Dog.prototype.bark = function () {
  console.log('Woof!');
};
let beagle = new Dog();

beagle.eat();
beagle.bark();