type tuple - nberlette/is GitHub Wiki

@nick/is/type/tuple

IsTuple

Signature

export type IsTuple<T, True = true, False = false> = T extends
  readonly [] | readonly [unknown, ...unknown[]] ? True : False;

Resolves to True if A is a tuple, which is an array with a pre-determined length and type for each of its elements. This check does not resolve to True for arrays such as string[] or Array<number> (since they are not tuples), but does for [1, 2, 3]. Any other type of value will resolve to False.

Type Parameters
  • T
  • True (default: true)
  • False (default: false)
Category

Types

Examples

import type { IsTuple } from "@nick/is/type";

type A = IsTuple<[1, 2, 3]>; // true
type B = IsTuple<string[]>; // false
type C = IsTuple<Array<number>>; // false
import type { IsTuple } from "@nick/is/type";

// using the conditional type parameters in a custom type
type EnsureTuple<T> = IsTuple<T, T, never>;

type A = EnsureTuple<[1, 2, 3]>; // [1, 2, 3]
type B = EnsureTuple<readonly []>; // readonly []
type C = EnsureTuple<string[]>; // never
type D = EnsureTuple<Array<number>>; // never
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