Get response status code in a middleware

Question

I am building an app in which I am trying to build my own logging system for each request.

For each request, I'd like to log the timestamp, the method used, the route, and finally the response code that has been sent to the client.

I have the following code for the moment :

// index.js
const express = require('express');
const bodyParser = require('body-parser');
const cors = require('cors');

const app = express();
app.use(bodyParser.json());
app.use(cors());

app.use(require('./lib/logging'));

app.get('/', (req, res, next) => {
  res.send('hello world !');
});

app.listen(3001);

// ./lib/logging.js
const moment = require('moment');
const chalk = require('chalk');
const log = console.log;

module.exports = (req, res, next) => {
  let now = `[${chalk.green(moment().format('HH:mm:ss'))}]`;
  let method = chalk.magenta(req.method);
  let route = chalk.blue(req.url);
  let code = chalk.yellow(res.statusCode); // Always 200
  log(`${now} ${method} request received on ${route} ${code}`);
  next();
}

Unfortunately, even if I do res.status(201).send('hello world') It will always catch a 200 status code... Is there a way to catch any response outgoing to the client and fetch its status code ?

Answer 1

Using the finish event from the response was indeed the good solution. The problem was in the finish event callback, I just couldn't use the arrow function because it wouldn't bind the this keyword, and this is were was stored the response data.

So the following code is working :

// ./lib/logging.js

const moment = require('moment');
const chalk = require('chalk');
const log = console.log;

module.exports = (req, res, next) => {
  let now = `[${chalk.green(moment().format('HH:mm:ss'))}]`;
  let method = chalk.magenta(req.method);
  let route = chalk.blue(req.url);
  res.on('finish', function() {
    let code = chalk.yellow(this.statusCode);
    log(`${now} ${method} request received on ${route} with code ${code}`);
  })

  next();
}