Logging has many challenges. It is very important to be able to get the right logging messages for any given situation.

NPM Winston

Winston at npm

npm install winston --save

Goals

The following are the goals

• Ensure all log messages are handled.
• Development environment where all messages are saved to console and log file.
• Heroku environment where info, warn and error messages are saved to console.
• Production environment (Digital Ocean) where info, warn and error messages are saved to log file.

Configuration

Thus, the following information needs to be outside of the application

• Log level
• Environment
• Logging file

I have chosen the following

• Log Level = LOG_LEVEL

  • Development environment; debug
  • Heroku environment; info
  • Production environment; info

• Environment = LOG_ENV

  • Development environment; dev
  • Heroku environment; heroku
  • Production environment; production

• Logging file = LOG_FILE

  • Development environment; log file must be outside of workspace else it interferes with Nodemon.
  • Production environment; with other log files.

Note that LOG_LEVEL is independent. This is to allow for the setting of higher debug levels in a production environment. This may be required if in pursuit of a production problem.

Configuration Data

I have chosen to store in .env file. For example

LOG_LEVEL=debug
LOG_ENV=dev
# LOG_ENV=heroku
# LOG_ENV=prod
LOG_FILE=/Users/{logs}/tmp/logfile.txt

Loading Configuration Data

Start with server.js

const express = require('express');
const mongoose = require('mongoose');

const {PORT, DATABASE_URL} = require('./config/config');

const {logger} = require('./config/logger');

...

require('./config/middleware.express')(app);
logger.info('Application middleware is configured');

require('./config/routes')(app);
logger.info('Application routes have been loaded');

module.exports = {app, runServer, closeServer};
logger.info('Application is exported');

To load configuration data, config.js

require('dotenv').config();

exports.LOG_ENV = process.env.LOG_ENV || 'prod';

exports.LOG_LEVEL = process.env.LOG_LEVEL || 'info';

exports.LOG_FILE = process.env.LOG_FILE || 'logfile.txt';

Logger

As I needed many different instances of a logger, I rolled my own

const winston = require('winston');

const {LOG_LEVEL, LOG_ENV, LOG_FILE} = require('./config');

const consoleOptions = {
    level: LOG_LEVEL,
    handleExceptions: true,
    // json: true,
    colorize: true
};
const fileOptions = {
    level: LOG_LEVEL,
    filename: LOG_FILE,
    handleExceptions: true,
    // json: true,
    colorize: true
};

const logger = (function() {
    if (LOG_ENV === 'production') {
        return new(winston.Logger)({
            transports: [
                new (winston.transports.File)(fileOptions)
            ]
        });
    }
    else if (LOG_ENV === 'heroku') {
        return new(winston.Logger)({
            transports: [
                new(winston.transports.Console)(consoleOptions)
            ]
        });
    }
    return new(winston.Logger)({        // dev
        transports: [
            new(winston.transports.Console)(consoleOptions),
            new (winston.transports.File)(fileOptions)
        ]
    });
}());

logger.stream = {
    write: (message, encoding) => {
        logger.debug(message);
    }
};

module.exports = {
    logger
};

Thus, when the server starts, the correct logger is configured.

Usage

Add to list of requires

@requires logger

Get a reference

const {logger} = require('./config/logger');

Convention

I have chosen the following

• logger.info

  • when something happens, examples
    • Server starts or stops
    • Email sent
    • Record added/updated/deleted
    • Event
    • Useful running message

• logger.debug

  • traces only
    • careful to ensure no pid

• logger.error

  • error events of any kind
    • ensure full details

• logger.warn

  • not an error but may be important, for example
    • record should have been found but was not.
    • could not find a URL that should have existed.
    • problems reading from a URL, for example, RSS feed.

Morgan

For an Express app, I also use Morgan to log HTTP requests.

I wish to stream Morgan logging messages to Winston.

As shown above, server.js

...

require('./config/middleware.express')(app);
logger.info('Application middleware is configured');

...

Morgan is middleware and so is loaded by middleware.express.js. Only the essentials are shown

const morgan = require('morgan');
const {logger} = require('./logger');
app.use(morgan('common', {stream: logger.stream}));

Thus Morgan messages will use logger.stream

logger.stream = {
    write: (message, encoding) => {
        logger.debug(message);
    }
};

which uses Winston logging to stream Morgan logging at level 'debug'.

Browser Logs

A simple trick to turn off console.log messages in the browser

globals.js

var hasConsole = false;
if (!hasConsole) {
  console.log = function() {};
}

globals.js is the first thing invoked.