freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/build-javascript-objects.md

---
id: 56bbb991ad1ed5201cd392d0
title: Build JavaScript Objects
challengeType: 1
videoUrl: 'https://scrimba.com/c/cWGkbtd'
forumTopicId: 16769
dashedName: build-javascript-objects
---

# --description--

You may have heard the term `object` before.

Objects are similar to `arrays`, except that instead of using indexes to access and modify their data, you access the data in objects through what are called `properties`.

Objects are useful for storing data in a structured way, and can represent real world objects, like a cat.

Here's a sample cat object:

```js
var cat = {
  "name": "Whiskers",
  "legs": 4,
  "tails": 1,
  "enemies": ["Water", "Dogs"]
};
```

In this example, all the properties are stored as strings, such as - `name`, `legs`, and `tails`. However, you can also use numbers as properties. You can even omit the quotes for single-word string properties, as follows:

```js
var anotherObject = {
  make: "Ford",
  5: "five",
  "model": "focus"
};
```

However, if your object has any non-string properties, JavaScript will automatically typecast them as strings.

# --instructions--

Make an object that represents a dog called `myDog` which contains the properties `name` (a string), `legs`, `tails` and `friends`.

You can set these object properties to whatever values you want, as long as `name` is a string, `legs` and `tails` are numbers, and `friends` is an array.

# --hints--

`myDog` should contain the property `name` and it should be a `string`.

```js
assert(
  (function (z) {
    if (
      z.hasOwnProperty('name') &&
      z.name !== undefined &&
      typeof z.name === 'string'
    ) {
      return true;
    } else {
      return false;
    }
  })(myDog)
);
```

`myDog` should contain the property `legs` and it should be a `number`.

```js
assert(
  (function (z) {
    if (
      z.hasOwnProperty('legs') &&
      z.legs !== undefined &&
      typeof z.legs === 'number'
    ) {
      return true;
    } else {
      return false;
    }
  })(myDog)
);
```

`myDog` should contain the property `tails` and it should be a `number`.

```js
assert(
  (function (z) {
    if (
      z.hasOwnProperty('tails') &&
      z.tails !== undefined &&
      typeof z.tails === 'number'
    ) {
      return true;
    } else {
      return false;
    }
  })(myDog)
);
```

`myDog` should contain the property `friends` and it should be an `array`.

```js
assert(
  (function (z) {
    if (
      z.hasOwnProperty('friends') &&
      z.friends !== undefined &&
      Array.isArray(z.friends)
    ) {
      return true;
    } else {
      return false;
    }
  })(myDog)
);
```

`myDog` should only contain all the given properties.

```js
assert(
  (function (z) {
    return Object.keys(z).length === 4;
  })(myDog)
);
```

# --seed--

## --after-user-code--

```js
(function(z){return z;})(myDog);
```

## --seed-contents--

```js
var myDog = {
// Only change code below this line


// Only change code above this line
};
```

# --solutions--

```js
var myDog = {
  "name": "Camper",
  "legs": 4,
  "tails": 1,
  "friends": ["everything!"]
};
```