Gain insights into Express.js essentials, routing, middleware, and RESTful APIs. Learn to integrate MongoDB, JWT authentication, validation, real-time features, and logging for scalable back-end apps.

Become a MERN Stack Developer

Express.js is a popular Node.js framework, especially useful for building APIs and server-side apps. It’s lightweight, unopinionated, and flexible, giving you full control over how your app is structured. Whether new to backend development or ready to build production-grade services using JavaScript, Express is a great place to start.

This module begins with a quick review of Node.js and asynchronous JavaScript. Then, we’ll cover Express.js essentials like routing, middleware, and modular app structure. We’ll learn to build RESTful APIs, connect our app to a database, and implement JSON web tokens (JWT) authentication. We’ll also explore validation and sanitization for added security. Finally, we’ll understand templating engines, real-time features using Socket.IO, and structured logging using Winston.

By the end of this module, we'll have a solid grasp of Express.js and the confidence to build secure, scalable, production-ready backend applications tailored to our own learning goals.

Node.js and Express

To reduce the complexity of the hashing algorithm

To ensure that identical passwords have different hashes

To allow the password to be decrypted later

Why is it important to use a salt when hashing passwords?

Why is it important to use a salt when hashing passwords?

It allows attackers to discover which usernames are valid.

What is a potential security risk of using detailed error messages during login failures?

What is a potential security risk of using detailed error messages during login failures?

JWTs reduce server-side session management overhead.

JWTs encrypt user data during transmission.

JWTs eliminate the need for database queries.

JWTs prevent cross-site scripting (XSS) attacks.

What is the primary advantage of using JWTs instead of session-based authentication in Express.js?

What is the primary advantage of using JWTs instead of session-based authentication in Express.js?

What is *not* a valid part of a JWT structure?

What is not a valid part of a JWT structure?

In the `Authorization` header with a `Bearer` prefix

Where should a JWT typically be included when making a request to a protected endpoint?

Where should a JWT typically be included when making a request to a protected endpoint?

It continues to work but with altered payload.

It is rejected by the server during verification.

It automatically regenerates with a new signature.

What happens if a JWT is tampered with by a malicious user?

What happens if a JWT is tampered with by a malicious user?

`const user = jwt.verify(token, secret);`

`const user = jwt.encrypt(token, secret);`

Which line correctly verifies and decodes a JWT in Express given the following setup?

```js
const token = req.headers.authorization?.split(' ')[1];
const secret = process.env.JWT_SECRET;
```

Which line correctly verifies and decodes a JWT in Express given the following setup?
<pre><code class="language-js">const token = req.headers.authorization?.split(' ')[1];
const secret = process.env.JWT_SECRET;
</code></pre>

To encrypt tokens before sending them to the client

To verify JWTs and attach the decoded user data to the request object

To hash user passwords before saving them

To check user roles and deny access to unauthorized roles

What is the primary responsibility of JWT authentication middleware in an Express.js app?

What is the primary responsibility of JWT authentication middleware in an Express.js app?

`req.headers['user'] = jwt.verify(token, secret)`

`req.authToken = jwt.sign(token, secret)`

While writing middleware for JWT authentication, what's the correct way to attach the decoded token data to the request object so it can be accessed in later route handlers?

While writing middleware for JWT authentication, what’s the correct way to attach the decoded token data to the request object so it can be accessed in later route handlers?

What is the main security concern addressed by `express-rate-limit`?

What is the main security concern addressed by <code>express-rate-limit</code>?

What does this CORS configuration do?

```js
app.use(
  cors({
    origin: "https://example.com",
  })
);
```

What does this CORS configuration do?
<pre><code class="language-js">app.use(
 cors({
 origin: &quot;https://example.com&quot;,
 })
);
</code></pre>

To strip directory paths and prevent path traversal attacks

Why is `path.basename(file.originalname)` used in the file name function of the multer storage configuration?

Why is <code>path.basename(file.originalname)</code> used in the file name function of the multer storage configuration?

Users can upload arbitrarily large files, risking DoS attacks.

Files larger than 1MB will be rejected by default.

All files will be compressed automatically.

What happens if you don’t set a `limits.fileSize` in your `multer` config?

What happens if you don’t set a <code>limits.fileSize</code> in your <code>multer</code> config?

They encrypt user input before execution.

They restrict queries to only predefined users.

They treat user input as data, not part of the SQL command.

What is the main reason parameterized queries prevent SQL injection?

What is the main reason parameterized queries prevent SQL injection?

It blocks requests from unknown IP addresses.

It formats MongoDB queries for consistency.

It removes query operators like `$ne`, `$gt` from user input.

How does `mongo-sanitize` help prevent NoSQL injection?

How does <code>mongo-sanitize</code> help prevent NoSQL injection?

`db.query("SELECT * FROM users WHERE username = '${user}'")`



`db.query("SELECT * FROM users WHERE username = ?", [user])`

Which option is a secure way to fetch a user using SQL based on username input?

Which option is a secure way to fetch a user using SQL based on username input?

It doesn’t include a content type header.

It uses `res.send()` instead of `res.render()`.

It directly embeds unsanitized user input in the response.

It does not use `await` with asynchronous code.

Why does this code pose an XSS risk?
```
res.send(`<h1>Welcome, ${req.query.name}</h1>`);
```

Why does this code pose an XSS risk?
<pre><code>res.send(`&lt;h1&gt;Welcome, ${req.query.name}&lt;/h1&gt;`);
</code></pre>

Evaluate your knowledge of securing Express applications using JWT, middleware, validation, and other best practices.

Node.js Essentials

Getting Started with Express.js

Diving Deeper into Routing

Mastering Middleware

Building RESTful APIs and Integrating Databases

Securing Your Express Applications

Beyond APIs: UI Rendering, Real-Time Communication, and Logging i

DevConnector Project

Conclusion

Quiz: Securing Express Apps