freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/object-oriented-programming/understand-the-constructor-property.english.md

id, title, challengeType, isHidden, forumTopicId

id	title	challengeType	isHidden	forumTopicId
587d7daf367417b2b2512b7e	Understand the Constructor Property	1	false	301327

Description

There is a special constructor property located on the object instances duck and beagle that were created in the previous challenges:

let duck = new Bird();
let beagle = new Dog();

console.log(duck.constructor === Bird);  //prints true
console.log(beagle.constructor === Dog);  //prints true

Note that the constructor property is a reference to the constructor function that created the instance. The advantage of the constructor property is that it's possible to check for this property to find out what kind of object it is. Here's an example of how this could be used:

function joinBirdFraternity(candidate) {
  if (candidate.constructor === Bird) {
    return true;
  } else {
    return false;
  }
}

Note
Since the constructor property can be overwritten (which will be covered in the next two challenges) it’s generally better to use the instanceof method to check the type of an object.

Instructions

Write a joinDogFraternity function that takes a candidate parameter and, using the constructor property, return true if the candidate is a Dog, otherwise return false.

Tests

tests:
  - text: <code>joinDogFraternity</code> should be defined as a function.
    testString: assert(typeof(joinDogFraternity) === 'function');
  - text: <code>joinDogFraternity</code> should return true if<code>candidate</code> is an instance of <code>Dog</code>.
    testString: assert(joinDogFraternity(new Dog("")) === true);
  - text: <code>joinDogFraternity</code> should use the <code>constructor</code> property.
    testString: assert(/\.constructor/.test(code) && !/instanceof/.test(code));

Challenge Seed

function Dog(name) {
  this.name = name;
}

// Only change code below this line
function joinDogFraternity(candidate) {

}

Solution

function Dog(name) {
  this.name = name;
}
function joinDogFraternity(candidate) {
  return candidate.constructor === Dog;
}