code: function setOutput(output) {
           if (!output ||
               typeof output.log !== 'function') {
               throw Error('logger.setOutput: expect an object as the parameter with "log" and "error" properties.');
           }
           outputFunctions = {
               log: output.log,
               error: (typeof output.error === 'function') ? output.error : output.log
           };
       }
docs: By default the `error` and `warn` levels log output to `console.error`, while all other
  levels log output to `console.log`.
  @param {Object} output - An object with 'log' and 'error' functions.
  @throws {Error}
  @example
  log.setOutput({
  error: myErrorStream
  log: myLogStream
  });