What is an array?
Almost everything you see in an app is a list: the products in a store, the messages in a chat, the songs in a playlist, the results of a search. All of those are arrays, and mastering them is half the battle won.
An array (list) is an ordered collection of values stored under a single name. Think of it as a row of numbered lockers, each one with a value inside.
Creating an array
const fruits = ["apple", "pear", "grape"];
const numbers = [10, 20, 30];
const empty = [];
An array can contain any type of data, even mixed.
Access by index
Each element has a position or index, which starts at 0:
console.log(fruits[0]); // "apple"
console.log(fruits[2]); // "grape"
console.log(fruits[9]); // undefined (doesn't exist)
You can modify an element by assigning to its index:
fruits[1] = "banana";
The length property
length indicates how many elements there are:
console.log(fruits.length); // 3
A common trick: the last element is at array[array.length - 1].
Examples
Accessing the first and last element
const colors = ["red", "green", "blue"];
console.log(colors[0]); // "red"
console.log(colors[colors.length - 1]); // "blue"
console.log("There are", colors.length, "colors");