Get all document pseudo-elements: a comparison

function getPseudoElementSelectors() {
    var matchPseudoSelector = /:{1,2}(after|before)/,
        found = { before: [], after: [] };

    if (!(document.styleSheets && document.styleSheets.length)) return found;

    return Array.from(document.styleSheets)
        .reduce(function(pseudoSelectors, sheet) {
            try {
                if (!sheet.cssRules) return pseudoSelectors;

                // Get an array of all individual selectors.
                var ruleSelectors = Array.from(sheet.cssRules)
                    .reduce(function(selectors, rule) {
                        return (rule && rule.selectorText)
                            ? selectors.concat(rule.selectorText.split(','))
                            : selectors;
                    }, []);

                // Construct a dictionary of rules with pseudo-elements.
                var rulePseudoSelectors = ruleSelectors.reduce(function(selectors, selector) {

                    // Check if this selector has a pseudo-element.
                    if (matchPseudoSelector.test(selector)) {
                        var pseudoElement = matchPseudoSelector.exec(selector)[1],
                            cleanSelector = selector.replace(matchPseudoSelector, '').trim();

                        selectors[pseudoElement].push(cleanSelector);
                    }

                    return selectors;
                }, { before: [], after: [] });

                pseudoSelectors.before = pseudoSelectors.before.concat(rulePseudoSelectors.before);
                pseudoSelectors.after = pseudoSelectors.after.concat(rulePseudoSelectors.after);

            // Quietly handle errors from accessing cross-origin stylesheets.
            } catch (e) { if (console && console.warn) console.warn(e); }

            return pseudoSelectors;

        }, found);
}

function getPseudoElementsByCssSelectors() {
    var selectors = getPseudoElementSelectors(),
        names = ['before', 'after']

    return names.reduce(function(pseudoElements, name) {
        if (!selectors[name].length) return pseudoElements;

        var selector = selectors[name].join(','),
            elements = Array.from(document.querySelectorAll(selector));

        return pseudoElements.concat(
            elements.reduce(function(withContent, el) {
                var pseudo = getComputedStyle(el, name);

                // Add to array if element has content defined.
                return (pseudo.content.length)
                    ? withContent.concat(pseudo)
                    : withContent;
            }, [])
        );
    }, []);
}

Array.from = Array.from || function(arrayish) {
    return [].slice.call(arrayish);
};

function getPseudoElements() {
        var allElements = document.getElementsByTagName("*"),
                pseudoElements = [];

        for (var i=0, max=allElements.length; i < max; i++) {
                var before = window.getComputedStyle(allElements[i], ':before');
                var after = window.getComputedStyle(allElements[i], ':after');
                if (before.content) {
                        pseudoElements.push(before);
                }
                if (after.content) {
                        pseudoElements.push(after);
                }
        }
        return pseudoElements;
}

console.time("getPseudoElementsByCssSelectors");
for (var i = 0; i < 1000; i++) getPseudoElementsByCssSelectors(); console.timeEnd("getPseudoElementsByCssSelectors");

console.time("getPseudoElements");
for (var i = 0; i < 1000; i++) getPseudoElements();
console.timeEnd("getPseudoElements");