isArrayOf function

Checks whether a value is an array whose every item passes a type guard.

import { isArrayOf } from 'utils';

Signature

export function isArrayOf<T>(value: unknown, guard: (item: unknown) => item is T): value is T[]

Parameters

Name	Description
T	Type of the items.
value	The value to check.
guard	The type guard applied to each item.

Returns

true for an array of T (an empty array included).

Example

isArrayOf([1, 2], isNumber); // true
isArrayOf([1, '2'], isNumber); // false

Tests

Line coverage: 100 %.

• ✅ checks every item

Source

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

Source code

/**
 * Checks whether a value is an array whose every item passes a type guard.
 *
 * @template T - Type of the items.
 * @param value - The value to check.
 * @param guard - The type guard applied to each item.
 * @returns `true` for an array of `T` (an empty array included).
 * @example
 * isArrayOf([1, 2], isNumber); // true
 * isArrayOf([1, '2'], isNumber); // false
 */
export function isArrayOf<T>(value: unknown, guard: (item: unknown) => item is T): value is T[] {
  return Array.isArray(value) && value.every((item: unknown) => guard(item));
}

Test file

import { isArrayOf } from './is-array-of';
import { isNumber } from './is-number';
import { isString } from './is-string';

describe(isArrayOf, () => {
  it('checks every item', () => {
    expect(isArrayOf([1, 2], isNumber)).toBe(true);
    expect(isArrayOf([], isNumber)).toBe(true);
    expect(isArrayOf([1, '2'], isNumber)).toBe(false);
    expect(isArrayOf('12', isString)).toBe(false);
  });
});

Keywords: is, array, of, guards, function