ElementOf type

Reads the item type of an array or tuple, such as the type of a const list of options.

import type { ElementOf } from 'utils';

Signature

export type ElementOf<T extends readonly unknown[]> = T[number];

Parameters

Name	Description
T	The array type.

Example

const UNITS = ['kn', 'km/h', 'm/s'] as const;
type Unit = ElementOf<typeof UNITS>; // 'kn' | 'km/h' | 'm/s'

Tests

Line coverage: 0 %.

• ✅ reads the item type

Source

src/types/element-of.ts (on GitHub)

Source code

/**
 * Reads the item type of an array or tuple, such as the type of a `const` list of options.
 *
 * @template T - The array type.
 * @example
 * const UNITS = ['kn', 'km/h', 'm/s'] as const;
 * type Unit = ElementOf<typeof UNITS>; // 'kn' | 'km/h' | 'm/s'
 */
export type ElementOf<T extends readonly unknown[]> = T[number];

Test file

import type { ElementOf } from './element-of';

describe('ElementOf', () => {
  it('reads the item type', () => {
    expectTypeOf<ElementOf<readonly ['kn', 'm/s']>>().toEqualTypeOf<'kn' | 'm/s'>();
    expectTypeOf<ElementOf<number[]>>().toEqualTypeOf<number>();
  });
});

Keywords: element, of, types, type