code: function attachFailHandler (yargs, handler) {
    yargs.fail((msg, err, usage) => {
      // If failure was handled previously, does nothing.
      if (errorHandled) {
        return;
      }
      handler(msg, err, usage);
      if (errorHandled) {
        // Workaround to avoid yargs from running the command.
        // Since yargs has no mechanisms to any error handler
        // alert the command execution needs to be stopped, and we can't
        // exit the process right away due to possible asynchronous
        // error handlers, we need a way to prevent the command to be
        // ran, since we are handling the error asynchronously.
        // Setting this inner flag will prevent yargs to run the command.
        yargs._setHasOutput();
      }
    });
  }
docs: Attaches an error handler into the Yargs instance.
  
  Guarantees the single error handling with the `errorHandled` flag,
  which can be set with the `setErrorHandled` function.
  
  @param {!Yargs} yargs The [Yargs]{@link https://github.com/yargs/yargs/blob/master/yargs.js}
  instance.
  @param {!Function} handler The error handler