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

---
id: 587d7daf367417b2b2512b7e
title: Understand the Constructor Property
challengeType: 1
forumTopicId: 301327
dashedName: understand-the-constructor-property
---

# --description--

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

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

console.log(duck.constructor === Bird); 
console.log(beagle.constructor === Dog);
```

Both of these `console.log` calls would display `true` in the console.

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:

```js
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`.

# --hints--

`joinDogFraternity` should be defined as a function.

```js
assert(typeof joinDogFraternity === 'function');
```

`joinDogFraternity` should return `true` if `candidate` is an instance of `Dog`.

```js
assert(joinDogFraternity(new Dog('')) === true);
```

`joinDogFraternity` should use the `constructor` property.

```js
assert(/\.constructor/.test(code) && !/instanceof/.test(code));
```

# --seed--

## --seed-contents--

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

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

}
```

# --solutions--

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