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A Blink only polyfill for Webkit's window.getMatchedCSSRules
// polyfill window.getMatchedCSSRules() in Chrome
if ( typeof window.getMatchedCSSRules !== 'function' ) {
var ELEMENT_RE = /[\w-]+/g,
ID_RE = /#[\w-]+/g,
CLASS_RE = /\.[\w-]+/g,
ATTR_RE = /\[[^\]]+\]/g,
// :not() pseudo-class does not add to specificity, but its content does as if it was outside it
PSEUDO_CLASSES_RE = /\:(?!not)[\w-]+(\(.*\))?/g,
PSEUDO_ELEMENTS_RE = /\:\:?(after|before|first-letter|first-line|selection)/g;
// convert an array-like object to array
function toArray (list) {
return [].slice.call(list);
}
// handles extraction of `cssRules` as an `Array` from a stylesheet or something that behaves the same
function getSheetRules (stylesheet) {
var sheet_media = stylesheet.media && stylesheet.media.mediaText;
// if this sheet is disabled skip it
if ( stylesheet.disabled ) return [];
// if this sheet's media is specified and doesn't match the viewport then skip it
if ( sheet_media && sheet_media.length && ! window.matchMedia(sheet_media).matches ) return [];
// get the style rules of this sheet
return toArray(stylesheet.cssRules);
}
function _find (string, re) {
var matches = string.match(re);
return re ? re.length : 0;
}
// calculates the specificity of a given `selector`
function calculateScore (selector) {
var score = [0,0,0],
parts = selector.split(' '),
part, match;
//TODO: clean the ':not' part since the last ELEMENT_RE will pick it up
while ( part = parts.shift(), typeof part == 'string' ) {
// find all pseudo-elements
match = _find(part, PSEUDO_ELEMENTS_RE);
score[2] = match;
// and remove them
match && (part = part.replace(PSEUDO_ELEMENTS_RE, ''));
// find all pseudo-classes
match = _find(part, PSEUDO_CLASSES_RE);
score[1] = match;
// and remove them
match && (part = part.replace(PSEUDO_CLASSES_RE, ''));
// find all attributes
match = _find(part, ATTR_RE);
score[1] += match;
// and remove them
match && (part = part.replace(ATTR_RE, ''));
// find all IDs
match = _find(part, ID_RE);
score[0] = match;
// and remove them
match && (part = part.replace(ID_RE, ''));
// find all classes
match = _find(part, CLASS_RE);
score[1] += match;
// and remove them
match && (part = part.replace(CLASS_RE, ''));
// find all elements
score[2] += _find(part, ELEMENT_RE);
}
return parseInt(score.join(''), 10);
}
// returns the heights possible specificity score an element can get from a give rule's selectorText
function getSpecificityScore (element, selector_text) {
var selectors = selector_text.split(','),
selector, score, result = 0;
while ( selector = selectors.shift() ) {
if ( element.webkitMatchesSelector(selector) ) {
score = calculateScore(selector);
result = score > result ? score : result;
}
}
return result;
}
function sortBySpecificity (element, rules) {
// comparing function that sorts CSSStyleRules according to specificity of their `selectorText`
function compareSpecificity (a, b) {
return getSpecificityScore(element, b.selectorText) - getSpecificityScore(element, a.selectorText);
}
return rules.sort(compareSpecificity);
}
//TODO: not supporting 2nd argument for selecting pseudo elements
//TODO: not supporting 3rd argument for checking author style sheets only
window.getMatchedCSSRules = function (element /*, pseudo, author_only*/) {
var style_sheets, sheet, sheet_media,
rules, rule,
result = [];
// get stylesheets and convert to a regular Array
style_sheets = toArray(window.document.styleSheets);
// assuming the browser hands us stylesheets in order of appearance
// we iterate them from the beginning to follow proper cascade order
while ( sheet = style_sheets.shift() ) {
// get the style rules of this sheet
rules = getSheetRules(sheet);
// loop the rules in order of appearance
while ( rule = rules.shift() ) {
// if this is an @import rule
if ( rule.styleSheet ) {
// insert the imported stylesheet's rules at the beginning of this stylesheet's rules
rules = getSheetRules(rule.styleSheet).concat(rules);
// and skip this rule
continue;
}
// if there's no stylesheet attribute BUT there IS a media attribute it's a media rule
else if ( rule.media ) {
// insert the contained rules of this media rule to the beginning of this stylesheet's rules
rules = getSheetRules(rule).concat(rules);
// and skip it
continue
}
//TODO: for now only polyfilling Gecko
// check if this element matches this rule's selector
if ( element.webkitMatchesSelector(rule.selectorText) ) {
// push the rule to the results set
result.push(rule);
}
}
}
// sort according to specificity
return sortBySpecificity(element, result);
};
}
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