JavaScript: arrays

An array stores an ordered collection of values. JavaScript uses zero-based indexes, so the first item is at index 0.

What you will learn

How to create and read an array
How to update an item and inspect its length
How indexes and missing items behave

Minimal example

const colors = ['red', 'green', 'blue'];
console.log(colors[0]); // "red"
colors[1] = 'lime';
console.log(colors.length); // 3

Use square brackets to read or update an item. The length property tells you how many positions the array currently contains.

Common mistakes

Do not use index 1 when you mean the first item; indexes start at zero.
An out-of-range index returns undefined; check that an item exists before using it.
Use array methods such as map, filter, and find when they express the operation clearly.