Getting started with arrays

Terminology

Array literal: A comma separated list of values surrounded by []. For example, ['cats', 'dogs', 'fish'].
Array index: The location of an item in an array. In Javascript, his is always a sequential number starting at 0.
Array item: Any Javascript data type (i.e. value) that an array index points to.
Array length: The number of items in an array. Accessed with the Array.length property.

Creating an array using const still allows you to change (or mutate) the items in that array.
```
const hobbies = ['pinball', 'bug hunting', 'napping'];
hobbies[2] = 'proper sleeping'; // No error!
```
- const only stops you from re-assigning hobbies, not changing hobbies.
The value of an element can be any data type: undefined, null, number, string, boolean, array, object, etc.
```
const randomStuff = [null, 9, 'Hello World!'];
```
- Although it's possible, you rarely see a mix of different value types in the same array.

Given the following array:

const animals = [
  'Puppy',
  'Bear',
  'Moose',
  'Coyote',
  'Tiger',
  'Husky'
];

You can retrieve an item from an array using the index:
```
const thirdAnimal = animals[2]; // Moose
```

The first index of an array is always 0.

const firstAnimal = animals[0]; // Puppy

The last index of an array is always Array.length - 1.

const lastAnimal = animals[animals.length - 1]; // Husky

To add an item to an array, the next index is always array.length.

animals[animals.length] = 'Wolf'; // New item at the end of the array