code: function splitFilesIntoBatches(files, config) {
      // We need to specifiy a different parser for TS files
      const configTS = Object.assign({}, config);
      configTS.parser = 'typescript';
  
      const batches = [];
  
      batches.push({
          files: files.filter(fileName => fileMatchesExtension(fileName, EXTENSIONS.js)),
          config: config,
      });
  
      batches.push({
          files: files.filter(fileName => fileMatchesExtension(fileName, EXTENSIONS.ts)),
          config: configTS,
      });
  
      return batches;
  }
docs: Takes a list of files and initial config, and splits into two batches, each consisting of a subset of files and
  the specific config for that batch.