freeCodeCamp/curriculum/challenges/en/02-javascript-algorithms-and-data-structures/object-oriented-programming/define-a-constructor-function.en.md

---
id: 587d7dad367417b2b2512b77
title: Define a Constructor Function
challengeType: 1
---

## Description
<section id='description'>
<code>Constructors</code> are functions that create new objects. They define properties and behaviors that will belong to the new object. Think of them as a blueprint for the creation of new objects.
Here is an example of a <code>constructor</code>:
<blockquote>function Bird() {<br>&nbsp;&nbsp;this.name = "Albert";<br>&nbsp;&nbsp;this.color = "blue";<br>&nbsp;&nbsp;this.numLegs = 2;<br>}</blockquote>
This <code>constructor</code> defines a <code>Bird</code> object with properties <code>name</code>, <code>color</code>, and <code>numLegs</code> set to Albert, blue, and 2, respectively.
<code>Constructors</code> follow a few conventions:
<ul><li><code>Constructors</code> are defined with a capitalized name to distinguish them from other functions that are not <code>constructors</code>.</li><li><code>Constructors</code> use the keyword <code>this</code> to set properties of the object they will create. Inside the <code>constructor</code>, <code>this</code> refers to the new object it will create.</li><li><code>Constructors</code> define properties and behaviors instead of returning a value as other functions might.</li></ul>
</section>

## Instructions
<section id='instructions'>
Create a <code>constructor</code>, <code>Dog</code>, with properties <code>name</code>, <code>color</code>, and <code>numLegs</code> that are set to a string, a string, and a number, respectively.
</section>

## Tests
<section id='tests'>

```yml
- text: <code>Dog</code> should have a <code>name</code> property set to a string.
  testString: 'assert(typeof (new Dog()).name === ''string'', ''<code>Dog</code> should have a <code>name</code> property set to a string.'');'
- text: <code>Dog</code> should have a <code>color</code> property set to a string.
  testString: 'assert(typeof (new Dog()).color === ''string'', ''<code>Dog</code> should have a <code>color</code> property set to a string.'');'
- text: <code>Dog</code> should have a <code>numLegs</code> property set to a number.
  testString: 'assert(typeof (new Dog()).numLegs === ''number'', ''<code>Dog</code> should have a <code>numLegs</code> property set to a number.'');'

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js

```

</div>



</section>

## Solution
<section id='solution'>


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

</section>