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@csstools/postcss-is-pseudo-class
Advanced tools
Readme
PostCSS Is Pseudo Class lets you use the :is
pseudo class function, following the
CSS Selector specification.
:is(input, button):is(:hover, :focus) {
order: 1;
}
Becomes :
input:hover {
order: 1;
}
input:focus {
order: 1;
}
button:hover {
order: 1;
}
button:focus {
order: 1;
}
Add PostCSS Is Pseudo Class to your project:
npm install @csstools/postcss-is-pseudo-class --save-dev
Use PostCSS Is Pseudo Class as a PostCSS plugin:
import postcss from 'postcss';
import postcssIsPseudoClass from '@csstools/postcss-is-pseudo-class';
postcss([
postcssIsPseudoClass(/* pluginOptions */)
]).process(YOUR_CSS /*, processOptions */);
PostCSS Is Pseudo Class runs in all Node environments, with special instructions for:
Node | Webpack | Gulp | Grunt |
---|
The preserve
option determines whether the original notation
is preserved. By default, it is not preserved.
postcss([
postcssIsPseudoClass({ preserve: true })
]).process(YOUR_CSS /*, processOptions */);
:is(input, button):is(:hover, :focus) {
order: 1;
}
Becomes :
input:hover {
order: 1;
}
input:focus {
order: 1;
}
button:hover {
order: 1;
}
button:focus {
order: 1;
}
:is(input, button):is(:hover, :focus) {
order: 1;
}
The specificityMatchingName
option allows you to change the selector used to adjust specificity.
The default value is does-not-exist
.
If this is an actual class, id or tag name in your code, you will need to set a different option here.
See how :not
is used to modify specificity.
postcss([
postcssIsPseudoClass({ specificityMatchingName: 'something-random' })
]).process(YOUR_CSS /*, processOptions */);
:is(.button, button):hover {
order: 7;
}
Becomes :
.button:hover {
order: 7;
}
button:not(.something-random):hover {
order: 7;
}
Warn on complex selectors in :is
pseudo class functions.
postcss([
postcssIsPseudoClass({ onComplexSelector: 'warning' })
]).process(YOUR_CSS /*, processOptions */);
Warn when pseudo elements are used in :is
pseudo class functions.
⚠️ Pseudo elements are always invalid and will be transformed to ::-csstools-invalid-<pseudo-name>
.
postcss([
postcssIsPseudoClass({ onPseudoElement: 'warning' })
]).process(YOUR_CSS /*, processOptions */);
:is(::after):hover {
order: 1.0;
}
/* becomes */
::-csstools-invalid-after:hover {
order: 1.0;
}
:is
takes the specificity of the most specific list item.
We can increase specificity with :not
selectors, but we can't decrease it.
Converted selectors are ensured to have the same specificity as :is
for the most important bit.
Less important bits can have higher specificity that :is
.
Before :
:is(:hover, :focus):is(.button, button) {
order: 7;
}
After :
/* specificity: [0, 2, 0] */
.button:hover {
order: 7;
}
/* specificity: [0, 2, 1] */
/* last bit is higher than it should be, but middle bit matches */
button:not(.does-not-exist):hover {
order: 7;
}
/* specificity: [0, 2, 0] */
.button:focus {
order: 7;
}
/* specificity: [0, 2, 1] */
/* last bit is higher than it should be, but middle bit matches */
button:not(.does-not-exist):focus {
order: 7;
}
Before :
:is(.alpha > .beta) ~ :is(:focus > .beta) {
order: 2;
}
After :
.alpha > .beta ~ :focus > .beta {
order: 2;
}
this is a different selector than expected as .beta ~ :focus
matches .beta
followed by :focus
.
avoid these cases.
writing the selector without :is()
is advised here
/* without is */
.alpha:focus > .beta ~ .beta {
order: 2;
}
If you have a specific pattern you can open an issue to discuss it. We can detect and transform some cases but can't generalize them into a single solution that tackles all of them.
FAQs
A pseudo-class for matching elements in a selector list
We found that @csstools/postcss-is-pseudo-class demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 3 open source maintainers collaborating on the project.
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