isNonEmptyArray function

Checks whether an array has an item, and narrows it so that its first item is defined.

import { isNonEmptyArray } from 'utils';

Signature

export function isNonEmptyArray<T>(items: readonly T[]): items is NonEmptyArray<T>

Parameters

Name	Description
T	The type of the items.
items	The array to check.

Returns

true when the array has an item.

Example

if (isNonEmptyArray(samples)) {
  const [first] = samples; // a sample, not `undefined`
}

Tests

Line coverage: 100 %.

• ✅ checks the length
• ✅ types the first item as defined

Source

src/guard/is-non-empty-array.ts (on GitHub)

Uses

• NonEmptyArray: An array with at least one item, so that its first item is never undefined.

Files it needs

src/guard/is-non-empty-array.ts imports, directly or not:

• src/types/non-empty-array.ts

Source code

import type { NonEmptyArray } from '../types';

/**
 * Checks whether an array has an item, and narrows it so that its first item is defined.
 *
 * @template T - The type of the items.
 * @param items - The array to check.
 * @returns `true` when the array has an item.
 * @example
 * if (isNonEmptyArray(samples)) {
 *   const [first] = samples; // a sample, not `undefined`
 * }
 */
export function isNonEmptyArray<T>(items: readonly T[]): items is NonEmptyArray<T> {
  return items.length > 0;
}

Test file

import type { NonEmptyArray } from '../types';
import { isNonEmptyArray } from './is-non-empty-array';

describe(isNonEmptyArray, () => {
  it('checks the length', () => {
    expect(isNonEmptyArray([0])).toBe(true);
    expect(isNonEmptyArray([])).toBe(false);
  });

  it('types the first item as defined', () => {
    expectTypeOf(isNonEmptyArray<number>).guards.toEqualTypeOf<NonEmptyArray<number>>();
  });
});

Keywords: is, non, empty, array, guards, function