Winston JSON Format Example

index.js

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

let test = {};

test.json = (args) => {
  const logger = createLogger({
    format: format.combine(
      format.timestamp(),
      format.json()
    ),
    transports: [
      new transports.File({
        filename: './info.log',
        level: 'info'
      })
    ]
  });
  logger.info({
    args: args,
    ...(process.memoryUsage())
  });
};

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

output.log

{"message":{"args":[],"rss":27086848,"heapTotal":11902976,"heapUsed":7414104,"external":42479},"level":"info","timestamp":"2018-08-30T04:55:10.898Z"}
{"message":{"args":["hello"],"rss":27086848,"heapTotal":11902976,"heapUsed":7412448,"external":42479},"level":"info","timestamp":"2018-08-30T04:55:13.859Z"}
{"message":{"args":["hello","world"],"rss":27070464,"heapTotal":11902976,"heapUsed":7415048,"external":42479},"level":"info","timestamp":"2018-08-30T04:55:16.202Z"}
{"message":{"args":["bye"],"rss":27107328,"heapTotal":11902976,"heapUsed":7414056,"external":42479},"level":"info","timestamp":"2018-08-30T04:55:20.380Z"}

package.json

{
  "name": "winston-json-format-example",
  "version": "1.0.0",
  "description": "Winston JSON 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"
  }
}