NonEmptyArray

An array type guaranteed to have at least one element. The first element resolves to T instead of T | undefined.

type Arr = NonEmptyArray<T>;

Usage

NonEmptyArray<T>

Use it when you want to express an array that can't be empty at the type level. An empty array isn't assignable, and accessing the first element always resolves to T, so you can use it without an undefined check.

import type { NonEmptyArray } from 'es-toolkit/types';

const a: NonEmptyArray<number> = [1, 2, 3]; // ok
const b: NonEmptyArray<number> = [1]; // ok
const c: NonEmptyArray<number> = []; // error: an empty array is not allowed.

function first<T>(arr: NonEmptyArray<T>): T {
  // The first element resolves to T, so no undefined check is needed.
  return arr[0];
}

Type Parameters

• T: The type of the elements.