Winston transports.File Example

index.js

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

let test = {};

test.common = (pretty, args) => {
  const output = (pretty
    ? format.prettyPrint()
    : format.simple());
  const logger = createLogger({
    format: format.combine(
      format.splat(),
      format.timestamp(),
      output
    ),
    transports: [
      new transports.File({
        filename: './info.log',
        level: 'info'
      }),
      new transports.File({
        filename: './error.log',
        level: 'error'
      })
    ]
  });
  if ((!!args) && (args.length > 0)) {
    logger.info('arguments: %o', args);
  } else {
    logger.error('Invalid arguments: %o', args);
  }
};

test.simple = (args) => (test.common(false, args));
test.pretty = (args) => (test.common(true, args));

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

output-pretty.md

info.log

{ level: 'error',
  message: 'Invalid arguments: [ [length]: 0 ]',
  timestamp: '2018-08-30T00:11:15.293Z',
  [Symbol(level)]: 'error',
  [Symbol(splat)]: [ [] ] }
{ '0': 'hello',
  level: 'info',
  message: 'arguments: [ \'hello\', [length]: 1 ]',
  timestamp: '2018-08-30T00:11:26.820Z',
  [Symbol(level)]: 'info',
  [Symbol(splat)]: [ [ 'hello' ] ] }
{ '0': 'hello',
  '1': 'world',
  level: 'info',
  message: 'arguments: [ \'hello\', \'world\', [length]: 2 ]',
  timestamp: '2018-08-30T00:11:36.403Z',
  [Symbol(level)]: 'info',
  [Symbol(splat)]: [ [ 'hello', 'world' ] ] }

error.log

{ level: 'error',
  message: 'Invalid arguments: [ [length]: 0 ]',
  timestamp: '2018-08-30T00:11:15.293Z',
  [Symbol(level)]: 'error',
  [Symbol(splat)]: [ [] ] }

output-simple.md

info.log

info: arguments: [ 'hello', [length]: 1 ] {"0":"hello","timestamp":"2018-08-30T00:09:46.253Z"}
info: arguments: [ 'hello', 'world', [length]: 2 ] {"0":"hello","1":"world","timestamp":"2018-08-30T00:09:59.756Z"}

error.log

error: Invalid arguments: undefined {"timestamp":"2018-08-30T00:09:18.115Z"}
error: Invalid arguments: [ [length]: 0 ] {"timestamp":"2018-08-30T00:09:33.387Z"}

package.json

{
  "name": "winston-transports-file-example",
  "version": "1.0.0",
  "description": "Winston transports.File 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"
  }
}