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import { parse } from 'css-tree';
function ensureSelectorList(node) {
if (node.type === 'Raw') {
return parse(node.value, { context: 'selectorList' });
}
return node;
}
function maxSpecificity(a, b) {
for (let i = 0; i < 3; i++) {
if (a[i] !== b[i]) {
return a[i] > b[i] ? a : b;
}
}
return a;
}
function maxSelectorListSpecificity(selectorList) {
return ensureSelectorList(selectorList).children.reduce(
(result, node) => maxSpecificity(specificity(node), result),
[0, 0, 0]
);
}
// §16. Calculating a selector’s specificity
// https://www.w3.org/TR/selectors-4/#specificity-rules
function specificity(simpleSelector) {
let A = 0;
let B = 0;
let C = 0;
// A selector’s specificity is calculated for a given element as follows:
simpleSelector.children.forEach((node) => {
switch (node.type) {
// count the number of ID selectors in the selector (= A)
case 'IdSelector':
A++;
break;
// count the number of class selectors, attributes selectors, ...
case 'ClassSelector':
case 'AttributeSelector':
B++;
break;
// ... and pseudo-classes in the selector (= B)
case 'PseudoClassSelector':
switch (node.name.toLowerCase()) {
// The specificity of an :is(), :not(), or :has() pseudo-class is replaced
// by the specificity of the most specific complex selector in its selector list argument.
case 'not':
case 'has':
case 'is':
// :matches() is used before it was renamed to :is()
// https://github.com/w3c/csswg-drafts/issues/3258
case 'matches':
// Older browsers support :is() functionality as prefixed pseudo-class :any()
// https://developer.mozilla.org/en-US/docs/Web/CSS/:is
case '-webkit-any':
case '-moz-any': {
const [a, b, c] = maxSelectorListSpecificity(node.children.first);
A += a;
B += b;
C += c;
break;
}
// Analogously, the specificity of an :nth-child() or :nth-last-child() selector
// is the specificity of the pseudo class itself (counting as one pseudo-class selector)
// plus the specificity of the most specific complex selector in its selector list argument (if any).
case 'nth-child':
case 'nth-last-child': {
const arg = node.children.first;
if (arg.type === 'Nth' && arg.selector) {
const [a, b, c] = maxSelectorListSpecificity(arg.selector);
A += a;
B += b + 1;
C += c;
} else {
B++;
}
break;
}
// The specificity of a :where() pseudo-class is replaced by zero.
case 'where':
break;
// The four Level 2 pseudo-elements (::before, ::after, ::first-line, and ::first-letter) may,
// for legacy reasons, be represented using the <pseudo-class-selector> grammar,
// with only a single ":" character at their start.
// https://www.w3.org/TR/selectors-4/#single-colon-pseudos
case 'before':
case 'after':
case 'first-line':
case 'first-letter':
C++;
break;
default:
B++;
}
break;
// count the number of type selectors ...
case 'TypeSelector':
// ignore the universal selector
if (!node.name.endsWith('*')) {
C++;
}
break;
// ... and pseudo-elements in the selector (= C)
case 'PseudoElementSelector':
C++;
break;
}
});
return [A, B, C];
};
export default specificity;
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