How do I declare a read-only array tuple in TypeScript?

Question

We can declare a typed tuple in TypeScript, for example, with the type annotation [string, number]. This means an array of 2 elements where the first element ne

Answer 1

Since the type [string, number] already is an Array, you can simply use:

Readonly<[string, number]>

Example:

let tuple: Readonly<[string, number]> = ['text', 3, 4, 'another text'];

tuple[0] = 'new text'; //Error (Readonly)

let string1: string = tuple[0]; //OK!
let string2: string = tuple[1]; //Error (Type number)
let number1: number = tuple[0]; //Error (Type string)
let number2: number = tuple[1]; //OK!
let number3: number = tuple[2]; //Error (Type any)