freeCodeCamp/curriculum/challenges/english/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();
duck.fly();

duck.eat() would display the string nom nom nom in the console, and duck.fly() would display the string 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');

The Dog prototype should have a bark() method.

assert('bark' in Dog.prototype);

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 the string nom nom nom

capture();
beagle.eat();
uncapture();
assert(logOutput == 'nom nom nom');

beagle.bark() should log the string Woof!

capture();
beagle.bark();
uncapture();
assert(logOutput == 'Woof!');

--seed--

--before-user-code--

var logOutput = "";
var originalConsole = console
function capture() {
    var nativeLog = console.log;
    console.log = function (message) {
        logOutput = message;
        if(nativeLog.apply) {
          nativeLog.apply(originalConsole, arguments);
        } else {
          var nativeMsg = Array.prototype.slice.apply(arguments).join(' ');
          nativeLog(nativeMsg);
        }
    };
}

function uncapture() {
  console.log = originalConsole.log;
}

capture();

--after-user-code--

uncapture();
(function() { return logOutput || "console.log never called"; })();

--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();