TypeScript arrays and tuples explained with examples

Arrays in TypeScript

Two equivalent ways to type an array:

// Both mean the same thing
const names: string[] = ["alice", "bob"];
const scores: Array = [98, 85, 91];

// Mixed types require a union
const mixed: (string | number)[] = ["a", 1, "b", 2];

TypeScript enforces the element type. Pushing the wrong type throws an error:

names.push(42); // Error: Argument of type 'number' is not assignable to parameter of type 'string'

Readonly arrays

const ids: readonly number[] = [1, 2, 3];
ids.push(4); // Error: Property 'push' does not exist on type 'readonly number[]'

Tuples

A tuple is a fixed-length array where each position has a specific type:

// [name, age, isAdmin]
const user: [string, number, boolean] = ["alice", 30, true];

const name = user[0]; // string
const age  = user[1]; // number

Tuples are useful for functions that return multiple values of different types:

function getCoords(): [number, number] {
  return [40.71, -74.00];
}
const [lat, lng] = getCoords();