Morgan for HTTP request logging in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Morgan default logging output

What is the output in the console when a GET request is made to '/' using Morgan's default format in an Express app?

Express

const express = require('express');
const morgan = require('morgan');
const app = express();
app.use(morgan('dev'));
app.get('/', (req, res) => res.send('Hello'));
app.listen(3000);

A :method :url :status :res[content-length] - :response-time ms

B GET / 404 0 - 0.000 ms

C GET / 200 5 - 1.234 ms

D GET / Hello 200 5 - 1.234 ms

💡 Hint

Morgan's 'dev' format shows method, url, status, response size, and response time.

Morgan's 'dev' format logs the HTTP method, URL, status code, response content length, and response time in milliseconds.

❓ Configuration

intermediate

Custom Morgan token usage

Which Morgan configuration correctly adds a custom token 'user-id' that logs the value of req.user.id?

Express

const morgan = require('morgan');
// Assume req.user.id exists

A

morgan.token('user-id', (req, res) => req.user.id);
app.use(morgan(':method :url :user-id'))

B

morgan.token('user-id', (res) => res.user.id);
app.use(morgan(':method :url :user-id'))

C

morgan.token('user-id', (req) => req.user.id);
app.use(morgan(':method :url :user-id'))

D

morgan.token('user-id', (req, res) => res.user.id);
app.use(morgan(':method :url :user-id'))

💡 Hint

Morgan tokens receive (req, res) arguments; user info is on req.

Morgan tokens are functions with (req, res) parameters. To access user id, use req.user.id.

❓ Troubleshoot

advanced

Morgan logs not appearing

An Express app uses Morgan for logging but no logs appear in the console when requests are made. What is the most likely cause?

A Morgan is configured with 'combined' format

B Morgan is used without calling app.use()

C Morgan is not installed via npm

D Morgan middleware is added after route handlers

💡 Hint

Middleware order matters in Express.

Morgan must be added before routes to log requests. If added after, requests are handled before logging.

🔀 Workflow

advanced

Conditional Morgan logging in production

How to configure Morgan to log requests only when NODE_ENV is 'development'?

Express

const morgan = require('morgan');
const express = require('express');
const app = express();

A app.use(morgan('dev'));

B app.use(morgan('dev', { skip: () => process.env.NODE_ENV !== 'development' }));

C app.use(morgan('dev')); if (process.env.NODE_ENV !== 'development') { app.disable('morgan'); }

D if (process.env.NODE_ENV === 'development') { app.use(morgan('dev')); }

💡 Hint

Morgan supports a skip option to conditionally skip logging.

Using the skip option with a function allows Morgan to skip logging when not in development.

✅ Best Practice

expert

Best practice for logging sensitive data with Morgan

Which approach is best to avoid logging sensitive information like authorization headers with Morgan?

A Create a custom Morgan token that excludes sensitive headers and use it in the format

B Use Morgan's 'combined' format and manually remove sensitive headers from logs later

C Disable Morgan logging entirely in production

D Log all headers but encrypt the log files

💡 Hint

Custom tokens allow control over what is logged.

Creating a custom token to exclude sensitive data ensures logs do not contain secrets while still logging useful info.