expose source names on Tumblr

exposeClassKeys.js

tumblr.getCssMap().then(cssMap => {
  const keys = Object.keys(cssMap);
  const elements = document.querySelectorAll("[class]");
  for (const {classList} of elements) {
    for (const className of classList) {
      const mappedClassName = keys.find(key => cssMap[key].includes(className));
      if (mappedClassName) classList.add(`tumblr--${mappedClassName}`);
    }
  }
});