Winston: Attempt to write logs with no transports

I'd try something like this, put all the logger related stuff into a module logger.js:

logger.js

var winston = require('winston');
var path = require('path');
    
// Set this to whatever, by default the path of the script.
var logPath = __dirname;
const tsFormat = () => (new Date().toISOString());
    
const errorLog = winston.createLogger({
    transports: [
        new winston.transports.File({
            filename: path.join(logPath, 'errors.log'),
            timestamp: tsFormat,
            level: 'info'
        })
    ]
});
    
const accessLog = winston.createLogger({
    transports: [
        new winston.transports.File({
            filename: path.join(logPath, 'access.log'),
            timestamp: tsFormat,
            level: 'info'
        })
    ]
});
      
    
module.exports = {
    errorLog: errorLog,
    accessLog: accessLog
};

and then test in index.js:

index.js

var logger = require('./logger');

logger.errorLog.info('Test error log');
logger.accessLog.info('Test access log');

You should see log lines like:

errors.log:

{"level":"info","message":"Test access log","timestamp":"2018-03-14T07:51:11.185Z"}

access.log:

{"level":"info","message":"Test error log","timestamp":"2018-03-14T07:51:11.182Z"}

EDIT

On Winston version 3.x.x, new (winston.Logger) has been replaced by winston.createLogger (https://github.com/bithavoc/express-winston/issues/175)

1 Logger + console logging for development purpose:

logger.js

var logPath = '';
var log_level = '';

const log = winston.createLogger({
  level: log_level,
  format: winston.format.json(),
  transports: [
    new winston.transports.File({
      filename: path.join(logPath, 'access.log'),
      timestamp: tsFormat,
      level: log_level
    }),
    new winston.transports.File({
      filename: path.join(logPath, 'error.log'),
      timestamp: tsFormat,
      level: 'error'
    }),
  ]
});

if (process.env.NODE_ENV !== 'production') {
  log.add(new winston.transports.Console({
    format: winston.format.simple()
  }));
}

module.exports = {
  log: log
};

app.js

const logger = require('./logger');

logger.log.info("starting application..");