How do I change my node winston JSON output to be single line

Question

When I create a nodejs winston console logger and set json:true, it always output JSON logs in multiline format. If I pipe these to a file and try to grep that file

Answer 1

winston.format.printf(
    info => `${info.timestamp} ${info.level}: ${JSON.stringify(info.message, null, 2)}`))

will pretty print the json object

Answer 2

"winston": "^3.0.0"

function createAppLogger() {
  const { combine, timestamp, printf, colorize } = format;

  return createLogger({
    level: 'info',
    format: combine(
      colorize(),
      timestamp(),
      printf(info => {
        return `${info.timestamp} [${info.level}] : ${JSON.stringify(info.message)}`;
      })
    ),
    transports: [new transports.Console()]
  });
}

Output:

2018-08-11T13:13:37.554Z [info] : {"data":{"hello":"Hello, World"}}

Answer 3

On "winston": "^3.2.1"

This is works great for me

const {createLogger, format} = require('winston');

// instantiate a new Winston Logger with the settings defined above
var logger = createLogger({

    format: format.combine(
      format.timestamp(),
      // format.timestamp({format:'MM/DD/YYYY hh:mm:ss.SSS'}),
      format.json(),
      format.printf(info => {
        return `${info.timestamp} [${info.level}] : ${info.message}`;
      })
  ),
  transports: [
    new winston.transports.File(options.file),
    new winston.transports.Console(options.console)
  ],
  exitOnError: false, // do not exit on handled exceptions
});

Answer 4

The winston transports provide a way to override the stringify method, so by modifying the config above I got single line JSON output.

New config:

winston = require('winston')
logger = new (winston.Logger)({
  transports: [
    new winston.transports.Console({
     json: true,
     stringify: (obj) => JSON.stringify(obj)
    })
  ]
})

Answer 5

winston 3.x (current version)

Default formatter

const winston = require('winston');
const logger = winston.createLogger({
  format: winston.format.json(),
  transports: [
    new winston.transports.Console()
  ]
});

Example

const test = { t: 'test', array: [1, 2, 3] };
logger.info('your message', test);
// logger output:
// {"t":"test","array":[1,2,3],"level":"info","message":"your message"}

Custom formatter

const winston = require('winston');

const { splat, combine, timestamp, printf } = winston.format;

// meta param is ensured by splat()
const myFormat = printf(({ timestamp, level, message, meta }) => {
  return `${timestamp};${level};${message};${meta? JSON.stringify(meta) : ''}`;
});

const logger = winston.createLogger({
  format: combine(
    timestamp(),
    splat(),
    myFormat
  ),
  transports: [
    new winston.transports.Console()
  ]
});

Example:

const test = { t: 'test', array: [1, 2, 3] };
// NOTE: wrapping object name in `{...}` ensures that JSON.stringify will never 
// return an empty string e.g. if `test = 0` you won't get any info if 
// you pass `test` instead of `{ test }` to the logger.info(...)
logger.info('your message', { test });
// logger output:
// 2018-09-18T20:21:10.899Z;info;your message;{"test": {"t":"test","array":[1,2,3]}}

winston 2.x (legacy version)

It seems that the accepted answer is outdated. Here is how to do this for current winston version (2.3.1):

var winston = require('winston');
var logger = new (winston.Logger)({
  transports: [
    new (winston.transports.Console)({
     json: true,
     stringify: (obj) => JSON.stringify(obj),
    })
  ]
})

Note the parenthesis around winston.transports.Console.