splat.js

const winston = require('../');
let { format } = winston;

/*
 * Simple helper for stringifying all remaining
 * properties.
 */
function rest(info) {
  return JSON.stringify(Object.assign({}, info, {
    level: undefined,
    message: undefined,
    splat: undefined,
    label: undefined
  }));
}

let logger = winston.createLogger({
  transports: [new winston.transports.Console({ level: 'info' })],
  format: format.combine(
    format.splat(),
    format.printf(info => `[${info.label}] ${info.message} ${rest(info)}`)
  )
});

logger.log(
  'info',
  'any message',
  {
    label: 'label!',
    extra: true
  }
);

logger.log(
  'info',
  'let\'s %s some %s',
  'interpolate',
  'splat parameters',
  {
    label: 'label!',
    extra: true
  }
);

logger.log(
  'info',
  'first is a string %s [[%j]]',
  'behold a string',
  { beAware: 'this will interpolate' },
  {
    label: 'label!',
    extra: true
  }
);

logger.log(
  'info',
  'first is an object [[%j]]',
  { beAware: 'this will interpolate' },
  {
    label: 'label!',
    extra: true
  }
);

//
// Non-enumerable properties (such as "message" and "stack" in Error
// instances) will not be merged into any `info`.
//
const terr = new Error('lol please stop doing this');
terr.label = 'error';
terr.extra = true;
logger.log(
  'info',
  'any message',
  terr
);

logger.log(
  'info',
  'let\'s %s some %s',
  'interpolate',
  'splat parameters',
  terr
);