Part 3.2Arrays, tuples and readonly data

Arrays

Put the element type before [] to describe an array. This makes accidental mixed collections obvious.

const scores: number[] = [12, 19, 25];
const names: Array<string> = ["Ada", "Lin"];

Tuples

A tuple describes a fixed-length collection where each position has a known type. It is ideal for small values such as coordinates.

const location: [number, number] = [55.9533, -3.1883];

Readonly data

Use readonly string[] for an array that a function may inspect but must not change. This lets a caller pass either a mutable or readonly array while keeping the function honest about mutation.