Typescript check whether a type is tuple or array

Question

type A = [1, 2, 3]
type B = (1|2|3)[]

type IsTuple<T> = ???

type C = IsTuple<A> // true
type D = IsTuple<B> // false

I am looking for a way to tell tuple and array type apart

Answer 1

This is the method I always use:

type IsTuple<T> = T extends [any, ...any] ? true : false

We can basically check if there are individual elements inside the tuple.

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Answer 2

update, I figured out the answer, by checking the length

type A = [1, 2, 3]
type B = (1|2|3)[]

type C = A['length'] //3
type D = B['length'] // number

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