How to use the @now/build-utils.FileBlob function in @now/build-utils

file =>
      !file.endsWith('.ts') &&
      !file.endsWith('.tsx') &&
      !file.match(libPathRegEx)
  );
  if (esmPaths.length) {
    const babelCompile = require('./babel').compile;
    for (const path of esmPaths) {
      const filename = basename(path);
      const { data: source } = await FileBlob.fromStream({
        stream: preparedFiles[path].toStream(),
      });

      const { code, map } = babelCompile(filename, source);
      shouldAddSourcemapSupport = true;
      preparedFiles[path] = new FileBlob({
        data: `${code}\n//# sourceMappingURL=${filename}.map`,
      });
      delete map.sourcesContent;
      preparedFiles[path + '.map'] = new FileBlob({
        data: JSON.stringify(map),
      });
    }
  }

  return {
    preparedFiles,
    shouldAddSourcemapSupport,
    watch: fileList,
  };
}