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')
})

Using Async Local Storage

You will most likely want to use async local storage to avoid passing the logger around in your code. See an example of how to do this here.