code: function getInputSources(pathname, callback) {
    let filesRead = 0;
    let sources = {};
  
    // test file is a file, the last section contains a extention period
    if (String(pathname).split('/').pop().indexOf('.') !== -1) {
      const searchPathname = pathname.substr(0, 2) === './' ? pathname.slice(2) : pathname;
  
      fs.readFile(searchPathname, 'utf8', (readFileError, fileData) => { // eslint-disable-line
        if (readFileError) {
          return callback(error(`while while getting input sources ${readFileError}`));
        }
  
        callback(null, { [searchPathname]: fileData });
      });
    } else {
      // get all file names
      dir.files(pathname, (filesError, files) => { // eslint-disable-line
        if (filesError) {
          return callback(error(`while while getting input sources ${filesError}`));
        }
  
        // if no files in directory, then fire callback with empty sources
        if (files.length === 0) {
          callback(null, sources);
        } else {
          // read all files
          dir.readFiles(pathname, (readFilesError, content, filename, next) => { // eslint-disable-line
            if (readFilesError) {
              return callback(error(`while getting input sources ${readFilesError}`));
            }
  
            // add input sources to output
            sources = Object.assign({}, sources, {
              [path.join('./', filename)]: content,
            });
  
            // increase files readFiles
            filesRead += 1;
  
            // process next file
            if (filesRead === files.length) {
              callback(null, sources);
            } else {
              next();
            }
          });
        }
      });
    }
  }
docs: Get all input source for a specific pathname, used for mapping config entry
  
  @method getInputSources
  @param {String} pathname a path string to a file or directory
  @param {Function} callback the final callback that returns the sources
  @callback {Object} sourceMap returns a source map for this pathname