winston-json-log-formatter

This is a very simple Node.js module which creates a console transport (by default) for winston to log messages in JSON format.

Requirements

• Node.js >= 8.3.0
• winston@3

Install

npm install winston-json-log-formatter

Usage/Features

Import the module in your source code which imports winston also.

const winston = require('winston');
const wjlf = require('winston-json-log-formatter');

Setup the console transport which will log in JSON.

wjlf.setupTransport(winston);

You can log dates automatically.

wjlf.setupTransport(winston, true);

Also you can bind properties to every log message.

wjlf.setupTransport(winston, false, { requestId: 'id' });

If you want to use the formatter only then you can access it via wjlf.logFormatter

How to log: just use winston.

winston.info('test message');
winston.info('message with meta object', { propertyOne: 1, propertyTwo: 'two' });

Example Lambda handler function

'use strict';
 
const winston = require('winston');
const wjlf = require('winston-json-log-formatter');
 
const handler = async (event, context) => {
  wjlf.setupTransport(winston, true, { awsRequestId: context.awsRequestId, foo: 'bar' });
 
  winston.log('info', 'starting', {
    nodeVersion: process.version,
    platform: process.platform,
    architecture: process.arch,
    timezoneOffset: new Date().getTimezoneOffset() / 60,
  });
 
  winston.info('test message');
 
  winston.error('error occurred', {
    error: {
      message: 'ERR_MSG',
      code: 145,
    },
  });
 
  return 'ok';
};
 
module.exports = {
  handler,
};

Output log messages are filterable in AWS CloudWatch Logs.

JSON

{"date":"2020-05-03T16:32:32.123Z","level":"info","message":"starting","meta":{"nodeVersion":"v12.16.1","platform":"linux","architecture":"x64","timezoneOffset":0},"awsRequestId":"fc121189-1778-40a0-882b-0f186f61285e","foo":"bar"}
{"date":"2020-05-03T16:32:32.160Z","level":"info","message":"test message","awsRequestId":"fc121189-1778-40a0-882b-0f186f61285e","foo":"bar"}
{"date":"2020-05-03T16:32:32.160Z","level":"error","message":"error occurred","meta":{"error":{"message":"ERR_MSG","code":145}},"awsRequestId":"fc121189-1778-40a0-882b-0f186f61285e","foo":"bar"}

AWS CloudWatch Logs

License

The MIT License (MIT)