Winston logging object

I had to combine the solution provided by @SherloxFR and @Anton.

const Winston = require('winston');
const { format } = Winston;

const options = {
    file: {
        ....
        format: format.combine(
            format.splat(), 
            format.json()
        ),
        ...
    },
    console: {
        ...
        format: format.combine(
            format.splat(),
            format.json()
        ),
        ...
    }
};

You can see that I added both format.splat() and format.json() to the options config in the above code.

const logger = new Winston.createLogger({
    transports: [
        new Winston.transports.File(options.file),
        new Winston.transports.Console(options.console)
    ],
    exitOnError: false // do not exit on handled exceptions
});

That is how I used the options config object. You can actually write the format code inside the transports array but I don't like it that way. It's your choice anyway.

After the configuration like that, the is how I used it in my code

let myObj = {
   name: "StackOverflow",
};

logger.info('Content: %o', myObj);

You can also spread it like this if you want

logger.info('Content: %o', {...myObj});

That's all. Winston should log your object with this set up.

You are trying to insert a JSON object directly into the string, so it will print [Object Object] without the JSON.stringify.

This is not fixable by configuring Winston, as this problem happens while the string is generated (before the logger.debug function actually reads it), so a console.log call would print the same thing.

The first parameter of the logger.* functions is the message (string), then you can pass a metadata object (JSON).

To use the metadata in your logFormat function, update your Logger instantiation as follow:

const winston = require('winston')
const { format, transports } = winston
const path = require('path')

const logFormat = format.printf(info => `${info.timestamp} ${info.level} [${info.label}]: ${info.message}`)

const logger = winston.createLogger({
  level: process.env.NODE_ENV === 'production' ? 'info' : 'debug',
  format: format.combine(
    format.label({ label: path.basename(process.mainModule.filename) }),
    format.timestamp({ format: 'YYYY-MM-DD HH:mm:ss' }),
    // Format the metadata object
    format.metadata({ fillExcept: ['message', 'level', 'timestamp', 'label'] })
  ),
  transports: [
    new transports.Console({
      format: format.combine(
        format.colorize(),
        logFormat
      )
    }),
    new transports.File({
      filename: 'logs/combined.log',
      format: format.combine(
        // Render in one line in your log file.
        // If you use prettyPrint() here it will be really
        // difficult to exploit your logs files afterwards.
        format.json()
      )
    })
  ],
  exitOnError: false
})

Usage:

const req = {
  body: {
    name: 'Daniel Duuch',
    email: '[email protected]',
    password: 'myGreatPassword'
  }
}

logger.debug(`Register ${req.body.name} with email ${req.body.email}`, { ...req.body, action: 'register' })

Console output:

2019-05-11 17:05:45 debug [index.js]: Register Daniel Duuch with email [email protected]

Logfile output (prettified by hand, see comment in the transport file format):

{
  message: 'Register Daniel Duuch with email [email protected]',
  level: 'debug',
  timestamp: '2019-05-11 17:05:45',
  label: 'index.js',
  metadata: {
    name: 'Daniel Duuch',
    email: '[email protected]',
    password: 'myGreatPassword',
    action: 'register'
  }
}

Hope this solves your issue.

Code for this answer

You can use format.splat() in your logger config:

const logger = createLogger({
    format: combine(
        ...
        format.splat(), // <--
        ...
    ),
    ...
});

...and log object using string interpolation:

let myObj = { /* ... */ };
logger.info('This message will include a complete object: %O', myObj);

My solution was to use this kind of formatter:

const { format } = winston
const consoleFormat = format.combine(
  format.prettyPrint(),
  format.splat(),
  format.printf((info) => {
    if (typeof info.message === 'object') {
      info.message = JSON.stringify(info.message, null, 3)
    }

    return info.message
  })
)

now all those options works as expected:

logger.info('plain text')
logger.info('plain text with object %o', { a:1, b: 2} )
logger.info({ a:1, b: 2 })