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

It is multi-threaded and uses parallel processing.

It uses a single-threaded, event-driven model with non-blocking I/O.

It processes requests synchronously, ensuring one completes before starting another.

What makes Node.js suitable for handling multiple concurrent requests efficiently?

What makes Node.js suitable for handling multiple concurrent requests efficiently?

Built-in modules must be installed using `npm` before use.

Custom modules must be placed inside the `node_modules` directory.

Third-party modules are installed via `npm` and listed in `package.json`.

The `require()` function is used to import modules only within ES Modules.

Which statement is *true* about Node.js modules?

Which statement is true about Node.js modules?

An error because `readFileSync` requires a callback function

Assuming `example.txt` contains the text "Hello, Node.js!", what is the output for the following code snippet?

```js
const fs = require('fs'); 
const data = fs.readFileSync('example.txt', 'utf8'); 
console.log(data);
```

Assuming <code>example.txt</code> contains the text “Hello, Node.js!”, what is the output for the following code snippet?
<pre><code class="language-js">const fs = require('fs'); 
const data = fs.readFileSync('example.txt', 'utf8'); 
console.log(data);
</code></pre>

```js
export function greet(name) {
  return `Hello, ${name}!`;
}
export function farewell(name) {
  return `Goodbye, ${name}!`;
}
```

```js
module.exports = greet;
module.exports = farewell;
```

```js
module.exports = { greet, farewell };
```

```js
require.exports = { greet, farewell };
```

How do you correctly export multiple functions from a custom CommonJS module in Node.js?



How do you correctly export multiple functions from a custom CommonJS module in Node.js?

It stores metadata about the project, including dependencies and scripts.

It automatically installs third-party packages when Node.js is installed.

It ensures that third-party modules work without needing `require()`.

It stores the source code of all third-party packages used by the project.

What is the primary purpose of the `package.json` file in a Node.js project?

What is the primary purpose of the <code>package.json</code> file in a Node.js project?

It will throw an error because `http` is not installed via npm.

It will start an HTTP server on port 3000, responding with `"Hello, World!"`.

It will create an HTTP server, but it won’t work because it does not specify a port.

It will return an HTML response instead of plain text.

What happens when the following Node.js script is executed?

```js
const http = require('http');

const server = http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('Hello, World!');
});

server.listen(3000, () => {
  console.log('Server running at http://localhost:3000');
});
```

What happens when the following Node.js script is executed?
<pre><code class="language-js">const http = require('http');

const server = http.createServer((req, res) =&gt; {
 res.writeHead(200, { 'Content-Type': 'text/plain' });
 res.end('Hello, World!');
});

server.listen(3000, () =&gt; {
 console.log('Server running at http://localhost:3000');
});
</code></pre>

To manage asynchronous operations and move tasks from the event queue to the call stack when it's empty

To create multiple threads for executing JavaScript code concurrently

To prioritize synchronous code execution over asynchronous code

What is the primary purpose of the event loop in JavaScript?

What is the primary purpose of the event loop in JavaScript?

"Start", then "Inside setTimeout" after five seconds, then "End"

"Start", then "End", then "Inside setTimeout" after five seconds

"Start", then "End", then "Inside setTimeout" immediately

"Start", then "Inside setTimeout" immediately, then "End"

What happens when the following code is executed?

```js
console.log("Start");

setTimeout(() => {
  console.log("Inside setTimeout");
}, 5000);

console.log("End");
```

What happens when the following code is executed?
<pre><code class="language-js">console.log(&quot;Start&quot;);

setTimeout(() =&gt; {
 console.log(&quot;Inside setTimeout&quot;);
}, 5000);

console.log(&quot;End&quot;);
</code></pre>

Because JavaScript doesn’t support nested functions

Because it is the only way to handle asynchronous operations

Because it makes code unreadable, hard to debug, and difficult to maintain

Because callbacks execute in parallel instead of sequentially

Why is deeply nested asynchronous code using callbacks referred to as callback hell?

Why is deeply nested asynchronous code using callbacks referred to as callback hell?

Promises always execute synchronously, making them faster.

Promises allow chaining, improving readability, and avoiding nested structures.

Promises execute in parallel, improving performance.

How does a promise improve handling asynchronous operations compared to callbacks?

How does a promise improve handling asynchronous operations compared to callbacks?

Blocks the entire program until the promise resolves

Suspends JavaScript’s event loop while waiting for the promise

Forces a function to return a resolved promise

Pauses execution of the surrounding `async` function until the promise resolves but doesn’t block other code

What does the `await` keyword do inside an `async` function?

What does the <code>await</code> keyword do inside an <code>async</code> function?

```js
const fetchData = async () => {
  const data = await someAsyncFunction();
  data.then((result) => {
      console.log(result);
    })
    .catch((err) => {
      console.error(err);
    });
}
```

```js
const fetchData = async () => {
  try {
    const data = await someAsyncFunction();
    console.log(data);
  } catch (err) {
    console.error(err);
  }
};
```

```js
const fetchData = async () => {
  const data = await someAsyncFunction();
  console.log(data);
  } catch (err) {
    console.error(err);
  }
}
```

```js
const fetchData = async () => {
  const data = await someAsyncFunction();
  console.log(data);
};
```

Which code snippet correctly handles errors when using `async`/`await`?

Which code snippet correctly handles errors when using <code>async</code>/<code>await</code>?

Test your knowledge of Node.js fundamentals and asynchronous JavaScript.

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: Node and Async Basics