mq4-hover-shim

A shim for the Media Queries Level 4 hover @media feature.

The CSSWG's Media Queries Level 4 Working Draft defines a hover media feature that can be used in media queries. This can be used to determine whether the user-agent's primary pointing device truly supports hovering (like mice do) (the hover value), or emulates hovering (e.g. via a long tap, like most modern touch-based mobile devices) (the on-demand value), or does not support hovering at all (like some old mobile devices) (the none value). This matters because emulated hovering typically has some ugly quirks, such as :hover being "sticky" (i.e. a hovered element stays in the :hover state even after the user stops interacting with it and until the user hovers over a different element). It is often better to avoid :hover styles in browsers where hovering supports is emulated.

However, since it's from a relatively recent Working Draft, the hover media feature is not supported in all current modern browsers or in any legacy browsers. So, this library was created to shim support for the feature into browsers that lack native support for it.

NOTE: This shim only adds support for the hover value of the hover media feature. So you can only tell the difference between "truly supports hovering" (the hover value)" and "does not truly support hovering" (the none or on-demand values).

The shim consists of two parts:

A PostCSS-based server-side CSS postprocessor that rewrites
```
@media (hover: hover) {
  some-selector {
      property: value;
  }
}
```
into
```
some-prefix some-selector {
  property: value;
}
```
(In normal use-cases, some-selector will contain the :hover pseudo-class and some-prefix will be a specially-named CSS class that will typically be added to the <html> element.)
A client-side JavaScript library that detects whether the user-agent truly supports hovering. When the check returns true, then your code can add the special CSS class to the appropriate element to enable :hover styles; for example:
```
$(document).on('mq4hsChange', function (e) {
  $(document.documentElement).toggleClass('some-special-class', e.trueHover);
});
```
Obviously, this requires JavaScript to be enabled in the browser, and would default to disabling :hover styles when JavaScript is disabled.

Installation

Via npm: npm install mq4-hover-shim
Via jspm: jspm install mq4-hover-shim

Client-side dependencies

The browser-side portion of the shim depends on jQuery for firing events.

Pull requests to add support for other browser event libraries would be welcomed.

Browser compatibility

The following is a summary of the results of testing the library in various browsers. Try out the Live Testcase.

Legend:

True positive - Browser supports real hovering, and mq4-hover-shim reports that it supports real hovering
True negative - Browser does NOT support real hovering, and mq4-hover-shim reports that it does NOT support real hovering
False negative - Browser supports real hovering, and mq4-hover-shim reports that it does NOT support real hovering
False positive - Browser does NOT supports real hovering, and mq4-hover-shim reports that it supports real hovering
??? - This case has yet to be tested.
Desktop - has a pointing device that supports true hovering (e.g. mouse, trackball, trackpad, joystick, http://xkcd.com/243/); lacks a touch-based pointing input device
Laplet - has both a pointing device that supports true hovering and a touch-based pointing input device
Mobile - has a touch-based pointing input device (e.g. touchscreen); lacks a pointing device that supports true hovering

Officially supported:

Blink (Chrome & recent Opera)
- Desktop - True positive in Chrome >=41; False negative in Chrome <41 due to Chromium bug #441613
- Laplet - ??? (Arguable true negative presumed)
- Mobile (Android) - True negative
Firefox
- Desktop - True positive
- Laplet - ??? (Arguable true negative presumed)
- Mobile (Android) - True negative
Android browser
- Mobile (Android 4.0/5.0) - True negative
- Laplet (Android 4.0/5.0) - ??? (Arguable true negative presumed)
Internet Explorer
- Desktop
- 11 - True positive
- 10 - True positive
- 9 - True positive
- 8 - True positive
- Laplet
- 11 - Arguable true negative
- Mobile (Windows Phone 8.1)
- 11
  - in mobile mode - True negative
  - in desktop mode - True negative
Safari (WebKit)
- Desktop (Safari 8 on OS X) - True positive
- Mobile (iOS 8.1) - True negative

Unofficially supported:

Presto
- Desktop (old Opera 12.1) - True positive
- Mobile (Opera Mini) - ??? (Theoretically: True negative)
- Mobile (Opera Mobile) - ??? (Theoretically: True negative)
Internet Explorer Mobile <=10 - ??? (Theoretically: True negative)

API

Node.js module; CSS postprocessor

The npm module has the following properties:

postprocessorFor
- Arguments: an options object with one property:
- hoverSelectorPrefix - This string will be prepended to all selectors within @media (hover: hover) {...} blocks within the source CSS.
  - Type: string
- Side-effects: none
- Return type: A PostCSS processor object (that was returned from a call to the postcss() function).
- Returns a CSS postprocessor that transforms the source CSS as described above.
featureDetector - Each of this object's properties is a string filepath to a JavaScript file containing the browser-side feature detector in a particular JavaScript module format.
- es6 - ECMAScript 6 module format (this is the original from which the other versions are generated)
- cjs - CommonJS module format
- umdGlobal - "enhanced" UMD module format; exports a window.mq4HoverShim global if the JS environment has no module system (e.g. if included directly via <script> in current browsers); (generated via Browserify's standalone option)

Browser-side feature detector

The browser-side feature detector is available in the following module formats:

ECMAScript 6: /src/browser/mq4-hover-shim.js
Raw CommonJS: /dist/cjs/mq4-hover-shim.js
UMD (Universal Module Definition) with global fallback: /dist/browser/mq4-hover-shim.js
- When this is used in a non-AMD non-CommonJS context, the module will be exported as a mq4HoverShim property on the global window object.

The module exports one public function:

supportsTrueHover()
- Arguments: none
- Side-effects: none
- Return type: boolean
- Returns a boolean value indicating if the browser's primary pointer currently supports true hovering or if the browser at least does not try to quirkily emulate hovering, such that :hover CSS styles are appropriate.
- In other words, returns true if @media (hover: hover) would evaluate to true were the browser to natively correctly implement Media Queries Level 4; otherwise, returns false.
- If the browser does not natively support the hover media feature, but does support touch via some pointing input device, then we define this touch-based pointer to be the "primary pointer". Hence, if said browser has multiple pointing input devices, one supporting touch and another supporting true hovering (e.g. the computer has both a mouse and a touchscreen), this function will return false, since the user could use the touch input device at any time and since :hover should only be used for progressive enhancement anyway.

The module has one public event:

Event name: mq4hsChange
- Fired whenever the primary pointer's support for true hovering changes.
- This may be due to a different pointer becoming the primary pointer, although that's not the only possible cause.
- This event isn't fired merely if a different pointer becomes the primary pointer. The new primary pointer must also differ from the old primary pointer in its support for true hovering. For example, switching from one mouse to another mouse, or from one touchscreen to another touchscreen won't cause this event to fire.
- Target: the document object
- Extra properties:
- trueHover
  - Type: boolean
  - Value: Same as supportsTrueHover()'s return value at the time of firing the event

Grunt, Gulp

Grunt: Use grunt-postcss to invoke the mq4-hover-shim CSS postprocessor via Grunt task.
Gulp: Use gulp-postcss to invoke the mq4-hover-shim CSS postprocessor via Gulp task.

Contributing

The project's coding style is laid out in the JSHint, ESLint, and JSCS configurations. Add unit tests when changing the CSS postprocessor. Lint and test your code using Grunt. Manually test any changes to the browser-side portion of the shim.

Also, please don't edit files in the dist subdirectory as they are generated via Grunt. You'll find source code in the src subdirectory!

Release History

See the GitHub Releases page for detailed changelogs.

(next release) - master
2015-01-18 - v0.0.4: Fix crash when CSS contains a media-type-only media query. Replaced postprocessor with postprocessorFor().
2015-01-14 - v0.0.3: Add jspm metadata. Improve docs.
2015-01-09 - v0.0.2: Many improvements. jQuery is now a dependency on the client side.
2014-12-31 - v0.0.1: Initial release

twbs / mq4-hover-shim

readme