code: function fileAppender(config, layout) {
    const appender = new FileAppender(config, layout);
  
    // push file to the stack of open handlers
    appenderList.push(appender);
  
    return appender.write;
  }
docs: File Appender writing the logs to a text file. Supports rolling of logs by size.
  
  @param file file log messages will be written to
  @param layout a function that takes a logevent and returns a string *   (defaults to basicLayout).
  @param logSize - the maximum size (in bytes) for a log file, *   if not provided then logs won't be rotated.
  @param numBackups - the number of log files to keep after logSize *   has been reached (default 5)
  @param compress - flag that controls log file compression
  @param timezoneOffset - optional timezone offset in minutes (default system local)
  @param stripAnsi - flag that controls if ansi should be strip (default true)