[] lets you use the :focus-within pseudo-class in CSS,
following the [Selectors Level 4 specification].
To use this feature you need to do two things :
- add the PostCSS plugin that transforms the selector into a class or attribute
- add the browser polyfill that sets the attribute or class on elements in a browser
<example.css>
/* becomes */
<example.expect.css>[] duplicates rules using the :focus-within pseudo-class
with a [focus-within] attribute selector, the same selector used by the
focus-within polyfill. This replacement selector can be changed using the
replaceWith option. Also, the preservation of the original :focus-within
rule can be disabled using the preserve option.
The preserve option determines whether the original notation
is preserved. By default, it is preserved.
<exportName>({ preserve: false })<example.css>
/* becomes */
<example.preserve-false.expect.css>The replaceWith option defines the selector to replace :focus-within. By
default, the replacement selector is [focus-within].
Please note that using a class, leverages classList under the hood which
might not be supported on some old browsers such as IE9, so you may need
to polyfill classList in those cases.
<exportName>({ replaceWith: '.focus-within' });<example.css>
/* becomes */
<example.replacewith.expect.css>Note that changing this option implies that it needs to be passed to the browser polyfill as well.
The disablePolyfillReadyClass option determines if selectors are prefixed with an indicator class.
This class is only set on your document if the polyfill loads and is needed.
By default this option is false.
Set this to true to prevent the class from being added.
<exportName>({ disablePolyfillReadyClass: true })<example.css>
/* becomes */
<example.disable-polyfill-ready-class.expect.css>import focusWithinInit from 'postcss-focus-within/browser';
focusWithinInit();or
<!-- When using a CDN url you will have to manually update the version number -->
<script src="https://unpkg.com/postcss-focus-within@<packageVersion>/dist/browser-global.js"></script>
<script>focusWithinInit()</script>[] works in all major browsers, including Safari 6+ and Internet Explorer 9+ without any additional polyfills.
The force option determines whether the library runs even if the browser
supports the selector or not. By default, it won't run if the browser does
support the selector.
focusWithinInit({ force: true });Similar to the option for the PostCSS Plugin, replaceWith determines the
attribute or class to apply to an element when it's considered to be :focus-within.
focusWithinInit({ replaceWith: '.focus-within });This option should be used if it was changed at PostCSS configuration level.
Given that Next.js imports packages both on the browser and on the server, you need to make sure that the package is only imported on the browser.
As outlined in the Next.js documentation, you need to load the package with a dynamic import:
useEffect(async () => {
const focusWithinInit = (await import('<packageName>/browser')).default;
focusWithinInit();
}, []);