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Express.js Framework

If Node.js is the "Environment," then Express.js is the "Framework." It is designed to make building web applications and APIs much easier and faster. At CodeHarborHub, we use Express because it is the industry standard for JavaScript backends.

1. Why use Express?​

Building a server using only built-in Node.js http module is like building a house by making your own bricks. Express gives you the bricks already made:

  • Easy Routing: Define what happens when a user visits /home vs /profile.
  • Middleware Support: Add extra features like logging or security with one line of code.
  • JSON Friendly: Perfect for talking to React frontends.

2. Setting Up Express​

First, create a folder for your project, initialize it, and install Express:

mkdir my-server
cd my-server
npm init -y
npm install express

3. The "Hello World" Server​

Create a file named server.js and add this code. This is the simplest Express server possible:

server.js
const express = require('express');
const app = express();
const PORT = 3000;

// This is a "Route"
app.get('/', (req, res) => {
  res.send('Welcome to the CodeHarborHub Server!');
});

app.listen(PORT, () => {
  console.log(`Server is running at http://localhost:${PORT}`);
});

To start it, run node server.js in your terminal. Open your browser and go to http://localhost:3000.

4. Understanding Request and Response​

Every route handler in Express gives you two important objects:

  1. req (Request): Information coming from the user (e.g., what they typed in a search bar).
  2. res (Response): What the server sends back to the user (e.g., text, HTML, or an image).

5. Handling Routes (The Roadmap)​

A "Route" is a combination of a URL and an HTTP Method. The most common methods are:

  • GET: To "Get" data (e.g., reading a blog post).
  • POST: To "Send" data (e.g., creating a new user account).
  • PUT: To "Update" data (e.g., changing your profile picture).
  • DELETE: To "Remove" data.
server.js
const express = require('express');
const app = express();
app.use(express.json());

app.get('/api/cricket', (req, res) => {
  res.json({ player: "MS Dhoni", shot: "Helicopter Shot" });
});

app.post('/api/login', (req, res) => {
  res.send("Processing login...");
});

6. Nodemon: The Developer's Best Friend​

Normally, every time you change your code, you have to stop and restart the server manually. Nodemon does this for you automatically!

Install it:

npm install -g nodemon

Run your server with it:

nodemon server.js
info

Installing packages globally with -g is generally discouraged for project-specific tools. It is better to install nodemon as a development dependency to ensure that all developers working on the project use the same version.

npm install --save-dev nodemon

Then, you can add a script to your package.json:

package.json
{
  "scripts": {
    "dev": "nodemon server.js"
  }
}

Now you can start your server with:

npm run dev

This way, everyone on the project will have the same version of nodemon, and you won't run into issues if someone doesn't have it installed globally.

Practice: The Dynamic Greeter​

Let's use URL Parameters to greet users by name!

server.js
const express = require('express');
const app = express();

app.get('/greet/:name', (req, res) => {
  const userName = req.params.name;
  res.send(`Hello ${userName}, welcome to the backend!`);
});

If you visit http://localhost:3000/greet/Ajay, the page will say "Hello Ajay, welcome to the backend!"

Middleware

Middleware functions are functions that have access to the request and response objects. They run before your route handler. A very common one is express.json(), which allows your server to read JSON data sent from the frontend.

server.js
app.use(express.json());