Logino

const logger = require('logino')
const log = logger({pid: process.pid} /* optional */, console.log)
 
log('Start')
// [{pid: ...}, 'Start']
 
const sublog = log.create('downstream' /* optional */)
 
sublog('Work')
// [{pid: ...}, 'downstream', 'Work']

If you need to queue the logs before an out function is ready, omit the out function from initialization:

const logger = require('logino')
const log = logger()
 
log('Start')
log('Work')
 
log.out(console.log)
// ['Start']
// ['Work']

log.out can also be paused with log.out(null), which will queue logs until it is re-routed by invoking log.out with a new function - e.g. log.out(console.error).

Features:

• Layered and functional (logs bubble up)

  Bring logging into the "small reusable packages" era that Node.js and npm popularized by supporting deeply nested logging while preserving context.

  This is especially useful with asynchronous work such as serving HTTP requests: multiple requests may be interleaved and thus a "request ID" logged at the beginning is not easily connected to e.g. a log from the database driver.

• Structured data

  To raise the bar to modern standards from text logging, we should encourage structured data like JSON.

• Formatting is deferred/external

  Decouple logging and formatting of logging. This library does no formatting.

• Convention over implementation

  If you publish code others might depend on and want it to log stuff, make it accept a log function as argument and use that.

  Move the choice of logging software up from deep libraries to DevOps or sysadmins.

• No super globals

Example

const logger = require('logino')
const log = logger({pid: process.pid}, console.log)
 
const srv = http.createServer((req, res) => {
  const requestId = headers['x-request-id']
 
  log({requestId, method: req.method, url: req.url})
 
  serveRequest(log.create({requestId}), req, res)
})
 
srv.listen(process.env.PORT)
srv.on('listening', () => log({listening: true, port: process.env.PORT}))
srv.on('close', () => log({closed: true}))
 
setTimeout(() => srv.close(), 10 * 1000)
 
function serveRequest(log, req, res) {
  getSomethingFromDb(req, (err, result) => {
    if (err) {
      log({txt: 'Failed to get stuff from DB', err})
      res.statusCode = 500
      res.end()
    } else {
      log('Completed')
      res.end(result)
    }
  })
}
 
/*
[{pid: 34996}, {listening: true, port: 8080}]
[{pid: 34996}, {requestId: '9c4631af9f983dd05d4ca247c9d9ed01', method: 'GET', url: '/'}]
[{pid: 34996}, {requestId: '99fdcb31640ed528752a5b3f7dd5ea9e', method: 'GET', url: '/'}]
[{pid: 34996}, {requestId: '99fdcb31640ed528752a5b3f7dd5ea9e'}, 'Completed']
[{pid: 34996}, {requestId: '9c4631af9f983dd05d4ca247c9d9ed01'}, {txt: 'Failed to get stuff from DB', err: ...}]
[{pid: 34996}, {closed: true}]
*/