LogLayer with Express

LogLayer can be easily integrated with Express as middleware to provide request-scoped logging via req.log. This guide will show you how to set it up.

Installation

First, install the required packages. You can use any transport you prefer - we'll use Pino in this example:

npm

npm i loglayer @loglayer/transport-pino pino express

pnpm

pnpm add loglayer @loglayer/transport-pino pino express serialize-error

yarn

yarn add loglayer @loglayer/transport-pino pino express serialize-error

Example

import express from 'express'
import pino from 'pino'
import { ILogLayer, LogLayer } from 'loglayer'
import { PinoTransport } from '@loglayer/transport-pino'
import { serializeError } from 'serialize-error';

// Create a Pino instance (only needs to be done once)
const pinoLogger = pino({
  level: 'trace' // Set to desired log level
})

const app = express()

// Add types for the req.log property
declare global {
  namespace Express {
    interface Request {
      log: ILogLayer
    }
  }
}

// Define logging middleware
app.use((req, res, next) => {
  // Create a new LogLayer instance for each request
  req.log = new LogLayer({
    transport: new PinoTransport({
      logger: pinoLogger
    }),
    errorSerializer: serializeError,
  }).withContext({
    reqId: crypto.randomUUID(), // Add unique request ID
    method: req.method,
    path: req.path,
    ip: req.ip
  })

  next()
})

// Use the logger in your routes
app.get('/', (req, res) => {
  req.log.info('Processing request to root endpoint')

  // Add additional context for specific logs
  req.log
    .withContext({ query: req.query })
    .info('Request includes query parameters')

  res.send('Hello World!')
})

// Error handling middleware
app.use((err: Error, req: express.Request, res: express.Response, next: express.NextFunction) => {
  req.log.withError(err).error('An error occurred while processing the request')
  res.status(500).send('Internal Server Error')
})

app.listen(3000, () => {
  console.log('Server started on port 3000')
})