Typescript weird type

Question

I've come across this type:

let a: [number | string];

I've googled and looked at the Typescript docs but I don't see this syntax mentioned. What is it, I see the base is a union of string or number but it's not a tuple nor is it an array. What does it correspond to? Can anyone explain in simple terms and how to initialise it and add values please.

Answer 1

It is a tuple of size 1. Contains either a number or a string