freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/object-oriented-programming/extend-constructors-to-receive-arguments.english.md

id, title, challengeType

id	title	challengeType
587d7dae367417b2b2512b79	Extend Constructors to Receive Arguments	1

Description

The Bird and Dog constructors from last challenge worked well. However, notice that all Birds that are created with the Bird constructor are automatically named Albert, are blue in color, and have two legs. What if you want birds with different values for name and color? It's possible to change the properties of each bird manually but that would be a lot of work:

let swan = new Bird();
swan.name = "Carlos";
swan.color = "white";

Suppose you were writing a program to keep track of hundreds or even thousands of different birds in an aviary. It would take a lot of time to create all the birds, then change the properties to different values for every one. To more easily create different Bird objects, you can design your Bird constructor to accept parameters:

function Bird(name, color) {
  this.name = name;
  this.color = color;
  this.numLegs = 2;
}

Then pass in the values as arguments to define each unique bird into the Bird constructor: let cardinal = new Bird("Bruce", "red"); This gives a new instance of Bird with name and color properties set to Bruce and red, respectively. The numLegs property is still set to 2. The cardinal has these properties:

cardinal.name // => Bruce
cardinal.color // => red
cardinal.numLegs // => 2

The constructor is more flexible. It's now possible to define the properties for each Bird at the time it is created, which is one way that JavaScript constructors are so useful. They group objects together based on shared characteristics and behavior and define a blueprint that automates their creation.

Instructions

Create another Dog constructor. This time, set it up to take the parameters name and color, and have the property numLegs fixed at 4. Then create a new Dog saved in a variable terrier. Pass it two strings as arguments for the name and color properties.

Tests

tests:
  - text: <code>Dog</code> should receive an argument for <code>name</code>.
    testString: assert((new Dog('Clifford')).name === 'Clifford', '<code>Dog</code> should receive an argument for <code>name</code>.');
  - text: <code>Dog</code> should receive an argument for <code>color</code>.
    testString: assert((new Dog('Clifford', 'yellow')).color === 'yellow', '<code>Dog</code> should receive an argument for <code>color</code>.');
  - text: <code>Dog</code> should have property <code>numLegs</code> set to 4.
    testString: assert((new Dog('Clifford')).numLegs === 4, '<code>Dog</code> should have property <code>numLegs</code> set to 4.');
  - text: <code>terrier</code> should be created using the <code>Dog</code> constructor.
    testString: assert(terrier instanceof Dog, '<code>terrier</code> should be created using the <code>Dog</code> constructor.');

Challenge Seed

function Dog() {

}

Solution

function Dog (name, color) {
  this.numLegs = 4;
  this.name = name;
  this.color = color;
}

const terrier = new Dog();