Winston Custom Format Example

index.js

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

let test = {};

const myFormat = (info) => (
  JSON.stringify(info)
);

test.custom = (args) => {
  const logger = createLogger({
    format: format.combine(
      format.splat(),
      format.timestamp(),
      format.printf(myFormat)
    ),
    transports: [
      new transports.File({
        filename: './info.log',
        level: 'info'
      })
    ]
  });
  logger.info('arguments: %o', args);
};

if (require.main === module) {
  const name = process.argv[2];
  const args = process.argv.slice(3);
  if (!name) {
    test.custom();
  } else {
    test[name](args);
  }
}

output.log

{"level":"info","message":"arguments: undefined","timestamp":"2018-08-30T00:26:07.483Z"}
{"0":"a","1":"b","2":"c","level":"info","message":"arguments: [ 'a', 'b', 'c', [length]: 3 ]","timestamp":"2018-08-30T00:26:41.984Z"}
{"0":"hello","1":"world","level":"info","message":"arguments: [ 'hello', 'world', [length]: 2 ]","timestamp":"2018-08-30T00:28:22.218Z"}

package.json

{
  "name": "winston-custom-format-example",
  "version": "1.0.0",
  "description": "Winston Custom Format Example",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "shinaisan@users.noreply.github.com",
  "license": "ISC",
  "dependencies": {
    "winston": "^3.0.0"
  }
}