@raymondwang/mock-match-media
v2.0.0
Published
Test utility for mocking `window.matchMedia` in JSDOM environments.
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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
viawindow.matchMedia
- Changing the value of media states using a mocked state
- Observing changes to media states with
addEventListener
,addListener
, andonchange
- Removing event listeners with
removeEventListener
andremoveListener
- Dispatching explicit events using
dispatchEvent
- Automatic environment cleanup between tests in Jest
Usage
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:
mockMedia
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:
mockMedia({
width: '1200px',
height: '800px',
});
clearMedia
Clears the mocked environment to its default values, without removing the mock.
In Jest, this is called automatically in each afterEach
block by default.
restoreMedia
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)
).