init(callback) {
    this.getFiles((success, error) => {
      if (error) handleMessage(msg['DIRECTORY_ERROR']);
      this.loadFiles((success, error) => {
        if (error) handleMessage(msg['GET_FILE_ERROR']);
        callback();
      });
    });
  }
Initialize file collection.
@method
@async
@param {function} callback - Callback function