not-ok.js

var bunyan = require('bunyan')
  , logger = null;

function thisIsNotOk() {
  logger = bunyan.createLogger(
    { name: 'test'
    , streams: [
      { type: 'rotating-file'
      , path: 'test.log' }]
    });
}

thisIsNotOk();

ok.js

var bunyan = require('bunyan')
  , logger = null;

function thisIsOk() {
  logger = bunyan.createLogger(
    { name: 'test'
    , streams: [{ stream: process.stdout }]
    });
}

thisIsOk();