Tuples

Tuples are arrays with a known length and a specific type at each index. Great for fixed-shape pairs, like `[name, age]`.

3 min read Level 2/5 #typescript#tuples#arrays

What you'll learn

Author a tuple type
Use optional and rest elements
Recognize when a tuple beats an object

A tuple is an array with a fixed length where each position has its own type.

The Syntax

let pair: [string, number] = ["Ada", 36];

pair[0];    // string
pair[1];    // number
pair[2];    // ✗ Tuple type '[string, number]' has no element at index '2'.

You set the length and types at each position. Beyond that, TS complains.

Named Tuple Elements

For readability, name the positions:

let user: [name: string, age: number] = ["Ada", 36];

The names are documentation only — the values are still accessed by index.

Common Use Cases

Return multiple values

function minMax(nums: number[]): [min: number, max: number] {
  return [Math.min(...nums), Math.max(...nums)];
}

const [min, max] = minMax([3, 1, 4]);

React-style state hook returns

function useToggle(): [boolean, () => void] {
  let on = false;
  const toggle = () => { on = !on; };
  return [on, toggle];
}

This is why const [count, setCount] = useState(0) works the way it does — useState returns a tuple.

Optional Elements

type Coord = [x: number, y: number, z?: number];

const a: Coord = [1, 2];
const b: Coord = [1, 2, 3];

Rest Elements

type Header = [name: string, ...values: string[]];

const h: Header = ["Authorization", "Bearer", "abc123"];

`readonly` Tuples

const pair: readonly [string, number] = ["Ada", 36];
pair[0] = "Grace";
// ~~~~~ Cannot assign to '0' because it is a read-only property.

Tuple vs Object — Which?

When	Use
Pair / triple where order is the meaning	Tuple
Many fields, named for clarity	Object
Multiple-return where caller destructures	Tuple
Anything you’d describe with names (“user”)	Object

Tuples shine for short, ordered returns. Objects shine when fields have semantic names.

Up Next

Objects — TypeScript’s everyday workhorse.

Objects →