dataAttrs.js

(function() {
  let props = $$('*')
    .filter(x => Object.keys(x.dataset).length)
    .reduce((o,x) => {
      Object.keys(x.dataset).forEach(key => {
        o[key] = key.replace(/[A-Z]/g, y => '-' + y.toLowerCase());
      });
      return o;
    }, {});

  return Object.keys(props)
    .reduce((o, x) => {
      let attr = 'data-' + props[x];
      o[attr] = $$('[' + attr + ']')
      return o;
    }, {});
}())