How Express builds on Node.js HTTP - Practice Exercises

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Express middleware do?

Consider this Express middleware function:

app.use((req, res, next) => {
  console.log(req.method);
  next();
});

What will be printed when a GET request is made to the server?

Express

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

app.use((req, res, next) => {
  console.log(req.method);
  next();
});

app.get('/', (req, res) => {
  res.send('Hello');
});

app.listen(3000);

A undefined

B POST

C GET

D Error

💡 Hint

Look at the request method property logged.

The middleware logs the HTTP method of the incoming request. For a GET request, it prints 'GET'.

📝 Syntax

intermediate

Identify the correct way to create an Express server using Node.js HTTP module

Which option correctly creates an Express app and starts a server using Node.js HTTP module?

Express

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

A http.createServer(app.listen(3000));

B

const server = http.createServer(app);
server.listen(3000);

C

app.createServer(http);
app.listen(3000);

D

const server = http.createServer();
server.listen(3000, app);

💡 Hint

Express apps can be passed as request listeners to Node.js HTTP servers.

Option B correctly passes the Express app as the request handler to http.createServer and then listens on port 3000.

🔧 Debug

advanced

Why does this Express app not respond to requests?

Given this code, why does the server not respond to requests?

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

app.get('/', (req, res) => {
  res.send('Hi');
});

// Missing app.listen call

Express

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

app.get('/', (req, res) => {
  res.send('Hi');
});

A Express requires a callback in app.get to be async

B The route handler is incorrect and causes an error

C The app needs to import http module to work

D The server never starts listening because app.listen is missing

💡 Hint

Check if the server is actually listening for requests.

Without calling app.listen, the Express app does not start a server and cannot respond to requests.

❓ state_output

advanced

What is the output of this Express app using Node.js HTTP server?

What will be the response body when a client requests '/'?

Express

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

app.get('/', (req, res) => {
  res.send('Welcome');
});

const server = http.createServer(app);
server.listen(3000);

A Welcome

B Cannot GET /

C Error: app is not a function

D Empty response

💡 Hint

Express app can be used as a request handler for Node.js HTTP server.

The HTTP server forwards requests to the Express app which sends 'Welcome' for '/' route.

🧠 Conceptual

expert

How does Express extend Node.js HTTP request and response objects?

Which statement best describes how Express builds on Node.js HTTP module?

A Express wraps Node.js HTTP request and response objects to add helper methods like res.send and req.params

B Express replaces Node.js HTTP module with its own implementation

C Express uses a different protocol than HTTP for requests and responses

D Express requires manual parsing of request body unlike Node.js HTTP

💡 Hint

Think about how Express adds convenience methods to the request and response.

Express extends the native Node.js HTTP objects by adding useful methods and properties to simplify handling requests and responses.