--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();