🚀 Day 11: Introduction to Express.js & REST API in Node.js

👨‍🏫 What You’ll Learn Today

• What is Express.js?

• Why use Express in Node.js?

• How to install and set up Express

• What is a REST API?

• Real-life mini project: Creating a basic REST API

• HTTP methods: GET, POST, PUT, DELETE

• FAQs

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🧾 What is Express.js?

Express.js is a fast, minimal, and flexible Node.js framework that makes it easier to build web servers and APIs.

Without Express: You manually handle http.createServer(), headers, routes
With Express: You just write simple and clean route handlers

✅ Think of Express like a shortcut to build backend apps quickly.

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📦 Why Use Express.js?

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🛠️ How to Install Express.js

Step 1: Create a new folder

mkdir express-intro
cd express-intro

Step 2: Initialize a Node project

npm init -y

Step 3: Install Express

npm install express

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✏️ Let’s Build a Simple REST API using Express.js

🌍 Project Idea: Manage a list of students

You’ll build a REST API that can:

• Add a student

• Get all students

• Update a student

• Delete a student

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📁 Folder Structure

express-intro/
├── index.js      <-- main file

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🧠 What is REST API?

REST stands for: REpresentational State Transfer

A REST API uses HTTP methods to perform actions on data:

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💻 Code: index.js (Full Example with Explanation)

// index.js

const express = require("express");
const app = express();
const port = 5000;

// In-memory database (array)
let students = [
  { id: 1, name: "Payal" },
  { id: 2, name: "Amit" },
];

// Middleware to parse JSON body
app.use(express.json());

// ✅ Route: GET all students
app.get("/students", (req, res) => {
  res.status(200).json(students);
});

// ✅ Route: POST - add new student
app.post("/students", (req, res) => {
  const { name } = req.body;

  if (!name) {
    return res.status(400).json({ error: "Name is required" });
  }

  const newStudent = {
    id: students.length + 1,
    name,
  };

  students.push(newStudent);
  res.status(201).json(newStudent);
});

// ✅ Route: PUT - update student
app.put("/students/:id", (req, res) => {
  const { id } = req.params;
  const { name } = req.body;

  const student = students.find((s) => s.id == id);

  if (!student) {
    return res.status(404).json({ error: "Student not found" });
  }

  student.name = name;
  res.json(student);
});

// ✅ Route: DELETE - remove student
app.delete("/students/:id", (req, res) => {
  const { id } = req.params;

  const index = students.findIndex((s) => s.id == id);

  if (index === -1) {
    return res.status(404).json({ error: "Student not found" });
  }

  students.splice(index, 1);
  res.json({ message: "Student deleted successfully" });
});

// Start the server
app.listen(port, () => {
  console.log(`🚀 Server is running at http://localhost:${port}`);
});

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▶️ How to Run the Project

node index.js

Now open browser or use Postman:

• GET http://localhost:5000/students → Get all students

• POST http://localhost:5000/students
  → body: { "name": "Ravi" }

• PUT http://localhost:5000/students/1
  → body: { "name": "Updated Name" }

• DELETE http://localhost:5000/students/1

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🧠 Error Handling Examples in Code

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❓ FAQs – Frequently Asked Questions

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1) Do I need Express for every project?

Not always. If you're only doing file read/write, plain Node is okay.
But for building APIs, Express saves a lot of time.

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2) What is app.use(express.json())?

It allows Express to understand JSON data sent in body of request.
Without this, req.body will be undefined.

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3) Can we connect this to a database?

Yes! We’re using an array for demo. In the next lessons, we’ll connect to MongoDB using Mongoose.

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4) What if I call PUT with a wrong ID?

Our code checks if student exists. If not, it returns:

{ "error": "Student not found" }

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5) Is this RESTful API?

✅ Yes. Each route follows REST principles:
GET, POST, PUT, DELETE on the resource /students.

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❗Problem: "I am not getting output in browser for POST, PUT, DELETE"

You're trying to perform:

• POST

• PUT

• DELETE

directly from the browser URL bar, but browser can only make GET requests from the address bar.

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✅ Simple Explanation

💻 What you can use the browser for:

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✅ What Should You Use Instead?

Use one of the following tools:

1️⃣ Postman (Recommended for students and professionals)

• Download: https://www.postman.com/downloads/

• Create requests:

  • Choose method: POST, PUT, DELETE

  • URL: http://localhost:5000/students

  • Set Body > raw > JSON

  • Example body:

      { "name": "Ravi" }
    

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2️⃣ Thunder Client (VS Code Extension)

• In VS Code, install "Thunder Client"

• Works just like Postman inside your code editor

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3️⃣ Build a Simple Frontend using HTML/JS to send fetch() requests

If you want, I can give you a very simple HTML frontend with buttons for:

• Add Student

• Edit Student

• Delete Student

• View All Students

Just let me know.

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✅ Summary

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📝 Practice for Students

• Add a new route: GET /students/:id

• Add email along with name in student object

• Add validation for email format

• Create a separate routes folder and move routes there (structure practice)

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✅ Summary

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