What Is Express.js?

Express.js is a lightweight web framework for Node.js.

It simplifies:

• Routing

• Request handling

• Responses

• Middleware

• APIs

Why Express Simplifies Node.js Development

Raw Node.js HTTP servers require more boilerplate.

Raw Node.js Server

const http = require("http");

const server = http.createServer((req, res) => {
  if (req.url === "/") {
    res.end("Home Page");
  }
});

server.listen(3000);

Express Server

const express = require("express");

const app = express();

app.get("/", (req, res) => {
  res.send("Home Page");
});

app.listen(3000);

Much cleaner and easier to read.

Install Express

npm install express

Creating Your First Express Server

const express = require("express");

const app = express();

app.listen(3000, () => {
  console.log("Server running");
});

What Is Routing?

Routing means deciding which code runs for a specific URL and HTTP method.

Example Routes

Request → Response Flow

Handling GET Requests

GET requests usually fetch data.

Example

const express = require("express");

const app = express();

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

app.listen(3000);

Visit

http://localhost:3000

Output

Welcome to Express

Understanding Route Handler

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

Breakdown

Express Routing Structure

Handling Multiple Routes

const express = require("express");

const app = express();

app.get("/", (req, res) => {
  res.send("Home Page");
});

app.get("/about", (req, res) => {
  res.send("About Page");
});

app.listen(3000);

Handling POST Requests

POST requests usually send data to server.

Examples:

• Login forms

• Registration

• Creating records

Example

const express = require("express");

const app = express();

app.post("/users", (req, res) => {
  res.send("User created");
});

app.listen(3000);

GET vs POST

Sending Responses

Express provides helpful response methods.

Sending Text

res.send("Hello");

Sending JSON

res.json({
  name: "Ali",
  age: 22
});

Example JSON Route

app.get("/user", (req, res) => {
  res.json({
    name: "Sara",
    city: "Lucknow"
  });
});

Output

{
  "name": "Sara",
  "city": "Lucknow"
}

Route Matching Example

Starting the Server

app.listen(3000, () => {
  console.log("Server started");
});

Running the Application

node app.js

Common Beginner Mistakes

Practical Example

const express = require("express");

const app = express();

app.get("/", (req, res) => {
  res.send("Home");
});

app.get("/products", (req, res) => {
  res.json([
    "Laptop",
    "Phone",
    "Keyboard"
  ]);
});

app.post("/products", (req, res) => {
  res.send("Product added");
});

app.listen(3000);

Key Takeaways

Final Notes

Express became popular because it makes backend development:

• Faster

• Cleaner

• Easier to maintain

Almost all Node.js backend applications use Express or frameworks built around similar routing concepts.