An array is a data structure that holds a collection of elements, such as numbers, strings, or objects, indexed by position.

An array is enclosed in square brackets [], and the entries are separated by a comma , .

let week = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]

It is possible to get and set the value of an array with index notation. The position of an element in the array is zero-indexed, it starts at 0 and goes until the length of the array -1

let day = week[0]
// Monday

day = week[1]
// Tuesday

day = week[6]
// Sunday

day = week[7]
// undefined

Working with arrays

There is a funny meme that says that in programming there are just 0, 1, or infinite things. To know how many things there are in an array you can read the array property length.

week.length
// 7

When working with arrays it's easy to think about a list of things. The kind of possible operations should be intuitive. We can add things to the list, and we can decide if at the beginning or the end, we can search for an item in the list, we can sort the list, we can do something for each element of the list, or map every entry to something different. And so on and so forth.

Find some useful references on the MDN documentation .

Arrays as touples

In Javascript, arrays can contain a mix of different data types, so for example some strings, some numbers, etc.

["Monday", "Tuesday", 1, 2, 3, "Saturday", "Sunday", true, false]

This is an approach that lets you use arrays as touples. It can be really helpful to work with simple data structures (think for example something like ['Bob', '27] , ['Alice', 29] where we have a list of [name, age]. The downside of this approach is that informations are not really explicit.

Even accessing the data is somehow a bit more obscure, see for example:

let person = ["Bob", 27]

let name = person[0]
let age = person[1]

// not exaclty the most clear, right?
// compare with the Object approach

person = {name: "Bob", age: 27}

name = person.name
age = person.age

// we have a bit more of context of what's happening!