JavaScript Arrays Explained

Arrays are container-like values that can hold other values. The values inside an array are called elements.

// EXAMPLE
var breakfast = ["coffee", "croissant"];
breakfast;

// OUTPUT
["coffee", "croissant"]

Array elements don’t all have to be the same type of value. Elements can be any kind of JavaScript value — even other arrays.

// EXAMPLE
var hodgepodge = [100, "paint", [200, "brush"], false];
hodgepodge;

// OUTPUT
[100, "paint", [200, "brush"], false]

Accessing Elements

To access one of the elements inside an array, you’ll need to use the brackets and a number like this: myArray[3]. JavaScript arrays begin at 0, so the first element will always be inside [0].

// EXAMPLE
var sisters = ["Tia", "Tamera"];
​sisters[0];

// OUTPUT
"Tia"

To get the last element, you can use brackets and `1` less than the array’s length property.

// EXAMPLE
var actors = ["Felicia", "Nathan", "Neil"];
​actors[actors.length - 1];

// OUTPUT
"Neil"

This also works for setting an element’s value.

// EXAMPLE
var colors = ["red", "yelo", "blue"];
​colors[1] = "yellow";
​colors;

// OUTPUT
["red", "yellow", "blue"]

Properties and methods

Arrays have their own built-in variables and functions, also known as properties and methods. Here are some of the most common ones.

length
An array’s length property stores the number of elements inside the array.

// EXAMPLE
["a", "b", "c", 1, 2, 3].length;

// OUTPUT
6

concat
An array’s concat method returns a new array that combines the values of two arrays.

// EXAMPLE
["tortilla chips"].concat(["salsa", "queso", "guacamole"]);

// OUTPUT
["tortilla chips", "salsa", "queso", "guacamole"]

pop
An array’s pop method removes the last element in the array and returns that element’s value.

// EXAMPLE
["Jupiter", "Saturn", "Uranus", "Neptune", "Pluto"].pop();

// OUTPUT
"Pluto"

push
An array’s push method adds an element to the array and returns the array’s length.

// EXAMPLE
["John", "Kate"].push(8);

// OUTPUT
3

reverse
An array’s reverse method returns a copy of the array in opposite order.

// EXAMPLE
["a", "b", "c"].reverse();

// OUTPUT
["c", "b", "a"]

Source

https://www.javascript.com/learn/arrays