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 :

```js
// 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: 
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 :

```js
// ./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();
}
```
The Express response [extends](https://github.com/expressjs/express/blob/508936853a6e311099c9985d4c11a4b1b8f6af07/lib/response.js#L42) the Node.js [`http.ServerResponse`](https://nodejs.org/api/http.html#http_class_http_serverresponse), so you can listen for the [`'finish'`](https://nodejs.org/api/http.html#http_event_finish) event:

> 
> ### Event: 'finish'
> 
> 
> Emitted when the response has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the operating system for transmission over the network. It does not imply that the client has received anything yet.
> 
> 
> 

```js
app.use((req, res, next) => {
  res.on('finish', () => {
    console.log(`Responded with status ${res.statusCode}`);
  });
  next();
});

```