worker.js

process((params, emit) => {

  const zip = new JSZip();
  const countryBlocksZip = 'GeoLite2-Country-CSV_20171003/GeoLite2-Country-Blocks-IPv4.csv';
  const countryLocationsZip = 'GeoLite2-Country-CSV_20171003/GeoLite2-Country-Locations-en.csv';

  emit(0);

  const parseFile = (zipFile, emitPre, emitPost) => {
    return zip
        .file(zipFile)
        .async('string')
        .then(data => {
          emit(emitPre);

          return new Promise((resolve, reject) => {
            Papa.parse(data, {
              header: true,
              error: reject,
              complete: results => {
                emit(emitPost);
                resolve(results);
              }
            })
          });
        })
  };

  zip
      .loadAsync(params.data)
      .then(zipContent => Promise.all([
        parseFile(countryBlocksZip, 25, 50),
        parseFile(countryLocationsZip, 75, 100)
      ]))
      .then(([ipv4, meta]) => {
        const dist = {};
        meta.data.forEach(geo => {
          dict[geo.geoname_id] = geo.country_name
        });

        return {
          ipv4: ipv4.data,
          meta: _.sortBy(meta.data, 'country_name'),
          dict: dict
        }
      })
});