isUndefined function

Checks whether a value is undefined; null does not pass.

import { isUndefined } from 'utils';

Signature

export function isUndefined(value: unknown): value is undefined

Parameters

Name	Description
value	The value to check.

Returns

true for undefined only.

Example

isUndefined(undefined); // true
isUndefined(null); // false

Tests

Line coverage: 100 %.

• ✅ accepts undefined only

Source

src/guard/is-undefined.ts (on GitHub)

Source code

/**
 * Checks whether a value is `undefined`; `null` does not pass.
 *
 * @param value - The value to check.
 * @returns `true` for `undefined` only.
 * @example
 * isUndefined(undefined); // true
 * isUndefined(null); // false
 */
export function isUndefined(value: unknown): value is undefined {
  return value === undefined;
}

Test file

import { isUndefined } from './is-undefined';

describe(isUndefined, () => {
  it('accepts undefined only', () => {
    expect(isUndefined(undefined)).toBe(true);
    expect(isUndefined(null)).toBe(false);
    expect(isUndefined(0)).toBe(false);
  });
});

Keywords: is, undefined, guards, function