code: function globExts() {
    let exts = _.flattenDeep(_.concat.apply(null, arguments));
    return (exts.length <= 1) ? (exts[0] && `.${exts[0]}` || ``) : `.{${exts.join(`,`)}}`;
  }
docs: Returns a wildcard glob pattern of the specified file extensions.
  
  @param {...(string|string[])} extensions - Extensions to be included in the
  wildcard pattern.
  
  @return {string} - Wildcard glob pattern consisting of all specified
  extensions.