Find Stylesheet Classes

rules.js

// Make one massive array of all the rules from the stylesheets on the page
const styleSheetRules = Object.keys(document.styleSheets).reduce((rules, i) => {
  const styleRules = document.styleSheets[i].cssRules || [];
  Object.keys(styleRules).forEach((j) => {
    rules.push(styleRules[j]);
  });
  return rules;
}, []);

// Function used to lookup the rules from the stylesheet
const findRules = (search) => {
  const rulesFound = styleSheetRules.reduce((items, rule) => {
    const selectorText = rule.selectorText;
    if (!selectorText) {
      return items;
    }
    if (selectorText.indexOf(search) > -1) {
      const classes = selectorText.split(',').forEach((i) => {
        const item = i.split(' ')[0].trim().replace('.','');
        if (item) {
          items.push(item);
        }
      });
    }
    return items;
  }, []);

  return Array.from(new Set(rulesFound)).sort();
}