mock-match-media

Test utility for mocking window.matchMedia in JSDOM environments.

JSDOM doesn't provide support for window.matchMedia, which means testing it in
Jest is pretty hard to do. Though the official documentation
offers a workaround, that solution doesn't allow us to simulate changes to
resolved media query values or trigger event listeners.

This utility mocks out the unsupported window.matchMedia function for a fully
mocked substitution, with support for:

- Creating a MediaQueryList via window.matchMedia
- Changing the value of media states using a mocked state
- Observing changes to media states with addEventListener, addListener, and onchange
- Removing event listeners with removeEventListener and removeListener
- Dispatching explicit events using dispatchEvent
- Automatic environment cleanup between tests in Jest

Usage

``ts
import { mockMedia } from '@raymondwang/mock-match-media';

it('should alert listeners when the user’s OS enters dark mode', () => {
const mediaQueryList = window.matchMedia('(prefers-color-scheme: dark)');
const spy = jest.fn();
mediaQueryList.addEventListener('change', spy);
// Mock the media state to indicate that the user prefers dark mode:
mockMedia({ 'prefers-color-scheme': 'dark' });
// Updating the mocked media state should call all listeners with changes:
expect(spy).toHaveBeenCalledWith(expect.objectContaining({ matches: true }));
});
`

See MDN for more examples on testing media queries.

API

This library exports three methods:

$3

Sets the value of a media feature in the mocked environment. For example, to
simulate a device with a width of 1200px and a height of 800px:

`ts
mockMedia({
width: '1200px',
height: '800px',
});
`

$3

Clears the mocked environment to its default values, without removing the mock.
In Jest, this is called automatically in each afterEach block by default.

$3

Calls clearMedia and restores the original value of window.matchMedia.
In Jest, this is called automatically in each afterAll block by default.

Support & caveats

This library is built against css-mediaquery,
which follows the Media Queries Level 3 spec.

This means it has out-of-the-box support for the following media features:

- type (all | screen | print)
- any-hover
- any-pointer
- aspect-ratio
- color-index
- color
- device-aspect-ratio (deprecated)
- device-height (deprecated)
- device-width (deprecated)
- display-mode
- grid
- height (min-, max-)
- hover
- inverted-colors
- monochrome
- orientation
- pointer
- prefers-color-scheme
- prefers-contrast
- prefers-reduced-data
- prefers-reduced-motion
- prefers-reduced-transparency
- resolution
- scan
- width (min-, max-)

It also supports compound media queries, like 'screen and (min-width: 1200px) and (max-width: 800px)',
or (prefers-color-scheme: dark), (monochrome)'.

However, it _does not_ support features proposed in the Level 4 draft,
such as comparison operators (e.g. (400px < width < 1000px)) or combining
media features with the or keyword (e.g. (pointer) or (hover)`).