Week 7 Day 5 challenges— Serving Static Files + fs module.

🔧 Challenge 1 — Make Your Own Mini Website With Express

Goal: Serve a small multi-page static website
Requirements:
Create a public/ folder with:
➙index.html
➙about.html
➙contact.html
➙A CSS file (styles.css)
Use express.static() to serve everything.
Add links between pages.
In index.html include a simple JavaScript file (main.js) that logs something to console.

What you must learn while solving:
➤How a server serves HTML/CSS/JS
➤Folder structure matters
➤Paths inside HTML (href, src)
➤That Express does NOT “touch” your HTML; it simply delivers files

📘 Challenge 2 — Build a “Notes API” with File Storage

Goal: Build an API that saves notes in a JSON file.
Requirements:
➙Create data/notes.json
➙Use fs.readFileSync and fs.writeFileSync
API Endpoints:
➙GET /notes → return all notes
➙POST /notes → add a new note Body contains { "title": "...", "content": "..." }
➙DELETE /notes/:id → delete a note by id
On server start:
➙If file does NOT exist, create it with [].

What you must learn:
➤How to read/write JSON files
➤How Express handles JSON bodies
➤How frontend (or Postman) interacts with an API
➤Error handling when reading broken JSON

📸 Challenge 3 — Create an Image Gallery (Static + Dynamic API)

Goal: Mix both static files AND APIs
Requirements:
➙Use a public/gallery/ folder that contains several images.
➙Serve them using express.static().
Make an API:
➙GET /api/images
→ return an array of image file names found in /public/gallery/
(Use fs.readdirSync to list files).
➙Create a frontend page (gallery.html) that:
➙Fetches /api/images
➙Displays all images dynamically using JavaScript

What you learn here:
➤How Express serves static assets
➤How to dynamically list files with fs
➤How frontend uses fetch() to get data from backend
➤Combining static HTML with dynamic API data

💥share your solutions in the group,
💥invite a friend,
      and as always —

💥stay well, stay curious, and stay coding ✌️

Week 7 Day 6: ⭐ Error Handling in Express
and
⭐ Environment Variables & Configurations

🌞 Good Afternoon Devs
Today we enter a very important part of backend development:
These two topics make your apps safe, predictable, and professional.
Without them, everything becomes chaos — like a city with no emergency system and no addresses.
Let’s start!

🚑 PART 1 — Error Handling in Express
When you build a server, errors WILL happen. Not maybe — absolutely, definitely, surely.
Your API might crash because:
➤File not found
➤JSON is broken
➤Database down
➤User sent invalid data
➤Logic error in your code
But Express gives us a structured way of dealing with errors.

🧨 1. What is an Error in Express?
Think of your Express app like a restaurant kitchen.
➙If everything is fine → Meals go out
➙If something burns, falls, spills → Errors happen
Errors must be:
➣Detected (you notice something is wrong)
➣Passed to the right handler
➣Handled cleanly (customer gets a nice explanation, not a disaster)
In code, this is the same:

throw new Error("Something went wrong!");
or
next(new Error("File missing!"));

🧩 2. Common Error Types
🔴 Type 1 — Syntax Errors
Mistakes in code.
console.log("Hello"
🟡 Type 2 — Runtime Errors
Something wrong during execution.
JSON.parse("broken json");
🔵 Type 3 — HTTP Errors
User sends wrong data:
➤Missing ID
➤Invalid query
➤Empty body
➤Unauthorized request
🟠 Type 4 — File System / Database Errors
Example:
fs.readFileSync("./data/missing.json");
File does not exist → Crash if unhandled.

🛠️ 3. How Express Normally Handles Errors
If you throw an error inside a route:
app.get("/test", (req, res) => { throw new Error("Boom!"); });
Express will crash your server unless you have special error middleware.

📣 4. Using next(err) to Pass Errors
This is like calling the restaurant manager when something goes wrong.

app.get("/user", (req, res, next) => { try { let user = JSON.parse("broken-json"); res.send(user); } catch (err) { next(err); // Pass it to error handler } });

Calling next(err) tells Express:

“Hey, something broke. Skip all remaining middlewares and send this error to the official error handler.”

🧯 5. Custom Error-Handling Middleware
This is the firefighter of your app.
🧠 Rule:
An error handler MUST have 4 arguments:

app.use((err, req, res, next) => { console.error(err.stack); res.status(500).json({ success: false, message: err.message, }); });

Why?
Express identifies error-handlers by (err, req, res, next) shape.

⚠️ 6. Sending Clean Error Responses
Instead of giving users ugly, confusing errors…
Bad response:
TypeError: Cannot read properties of undefined
Good response:
{ "success": false, "message": "User ID is required." }
This makes your API professional.
Example:

app.get("/item/:id", (req, res, next) => {
  if (!req.params.id) {
   return next(new Error("ID is missing.")); }
res.json({ id: req.params.id }); });

🧱 7. Common Mistakes
❌ Forgetting return before next(err)
This can cause multiple responses.
❌ Throwing error after sending res.send()
If you already sent a response, stop.
❌ Writing error handler before routes
Order matters in Express!

☑️Error handling helps you:
➤Prevent server crashes
➤Send helpful messages
➤Track issues
➤Debug easily
➤Keep users happy

🌍 PART 2 — Environment Variables & Configurations
Now imagine you have:
A development environment (your laptop)
A production environment (the real server)
They need different settings:
Setting    Development  Production  
port                   3000                   80
database          local                cloud
debuglogs        ON                  OFF  
API keys             fake                real   

This is why we use environment variables.

🔐 1. What Are Environment Variables?
Think of them like secret notes your app reads.
Example env variables:
➙PORT=3000 ➙DB_URL=mongodb://localhost:27017 ➙JWT_SECRET=super_secret_key
We keep them outside the code to protect secrets.

📦 2. Using dotenv in Express
➣Install:
npm install dotenv
➣Create .env file:
PORT=4000
MODE=development

Load dotenv inside server.js:

require("dotenv").config();
const port = process.env.PORT; console.log("App running on port:", port);

🧪 3. Why This Is Important
🔒 Security
You never want API keys inside GitHub.
💼 Different Machines = Different Settings
Your code runs everywhere without changes.
🛠️ Configurable Behavior
Turn features ON/OFF easily.

🏭 4. Dev vs Production Configurations
development:
➙console.log allowed
➙local database
➙detailed error messages
production:
➙no console logs
➙cloud database
➙clean error messages
We can do:

if (process.env.MODE === "development") { console.log("DEBUG MODE ON"); }

🚪 5. Setting Up the Server Port

const port = process.env.PORT || 3000; app.listen(port, () => { console.log(Server running on port ${port}); });

If .env has PORT=5000, it uses that.
If not, fallback to 3000.

🧭 6. Folder Setup Example
project/
         │ server.js
         │ .env
         │ package.json
         └── data/
         └── routes/
         └── public/

🟥 7. Common Mistakes
❌ Forgetting require("dotenv").config()
Variables will be undefined.
❌ Pushing .env to GitHub
NEVER do this.
❌ Using invalid names
Good:
API_KEY JWT_SECRET PORT
Bad:
my secret key

Week 7 Day 6 Challenges: (Error Handling + Environment Variables).

✅ Challenge 1 — Build an Error-Safe GET Endpoint
➤Create a route:
GET /user/:id
Requirements:
➙If id is not a valid number → send an error using next(err)
➙If id is less than 1 → send a custom error "Invalid ID"
➙If everything is valid → return { "message": "User found", "id": ... }
➤Add a global error-handling middleware to catch all errors
➤The error response must be clean, like: { "success": false, "message": "Invalid ID" }
Hint: Use isNaN(Number(id)) to check validity.

✅ Challenge 2 — Use dotenv to Configure Your App
Steps:
➤Create a .env file containing: ➙PORT=4000
➙MODE=development
➤Load environment variables using: require("dotenv").config();
➤Start your server using the port from .env
➤Print the mode: App running in development mode
➤Add a rule:
If MODE = "development" → console.log all requests
If MODE = "production" → no logs allowed
Hint: Use app.use() to create a simple logger middleware.

✅ Challenge 3 — Build an API That Reads a File Safely

➤Create a route:
GET /notes
➤Requirements:
Read notes.json using fs
➙If the file is missing → trigger an error using next(err)
➙If JSON is broken → catch the error and forward it to the error handler
➙If everything is fine → return the notes
➤Your global error middleware should send clean output: { "success": false, "message": "Could not read notes file" }
Hint: Use:
try { ... } catch(err) { next(err); }


💥share your solutions in the group,
💥invite a friend,
      and as always —

💥stay well, stay curious, and stay coding ✌️

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🚀 Week 7 Day 7 — Express Router & Useful NPM Packages

Alright campers 🔥💙
I hope you’re rested, hydrated, and still coding with curiosity. I apologize for not posting these weeks-life happened.
Today is our last lesson for Express basics before we move to even bigger things.
🌳 BIG IDEA:
When your project grows, all your routes in app.js become messy and hard to manage.
👉 The solution?
📦 Modularization
🛣️ Express Router
Just like a house has many rooms, your Express app should have many route files, not one chaotic room.

🧭 1️⃣ Why Router?
⚠️ PROBLEM: When your application grows:

app.get('/users')
app.post('/users')
app.get('/posts')
app.delete('/posts/:id')
app.put('/products/:id') ...


All inside app.js…
It becomes a mess 😵
🧠 Router allows you to split routes into logical files:

routes/users.js
routes/posts.js
routes/products.j

s

Each file handles only one thing → clean, organized code.

🛠️ 2️⃣ Create a Router

👉 Step 1: Create a folder
/routes
👉 Step 2: Create users.js

const express = require("express");
const router = express.Router();
// Routes

router.get("/", (req, res) => {
   res.send("Get all users"); });
router.post("/", (req, res) => {
   res.send("Create new user"); });
module.exports = router;

👉 Step 3: Use it in app.js

const usersRoute = require("./routes/users");
app.use("/users", usersRoute)

;

🎉 Now:
GET /users → gets all users
POST /users → creates new user
🪄 Cleaner, better, scalable.

📦 3️⃣ Another Example: posts.

js

const express = require("express");
const router = express.Router();
router.get("/", (req, res) => {
   res.send("All posts"); });
router.get("/:id", (req, res) => {
    res.send("Single post with ID " + req.params.id); });
module.exports = rout

er;

In app

.js:

const postsRoute = require("./routes/posts");
app.use("/posts", postsRo

ute);

Now you have:
/posts
/posts/123
💡 This is URL prefixing.

✨ 4️⃣ Benefits of Router
🔥 1. Clean code
🔥 2. Easier debugging
🔥 3. Can handle large projects
🔥 4. Can assign middleware per router
🔥 5. Can add separate controllers later

Imagine running a restaurant:
➙Kitchen
➙Cashier
➙Delivery
➙Cleaning
Each has their own place.
Same for routes.

🎯 Very Useful Pattern
Structure:

project/
       │ app.js
       │ package.json
       │
       ├─ routes/
               │
               ├─ users.js
               │
               ├─ posts.js
               │
       └─ controllers/
               ├─ usersController.js
               ├─ postsController.js

Later we will move logic from routes → controllers.

🧰 5️⃣ NPM Packages Commonly Used with Express
Below are must-know tools.
You’ll use them in almost every real backend.

1️⃣ morgan — Logging requests
Shows every request in console:
➙GET /users 200 12ms
➙ POST /login 401 5ms
Install:
npm install morgan
Use:
const morgan = require("morgan"); app.use(morgan("dev"));

2️⃣ cors — Cross Origin Resource Sharing
Frontend and backend are different origins.
If frontend is: http://localhost:5173 Backend is: http://localhost:3000
Browser blocks requests ❌ unless we allow.
Install:
npm install cors
Use:
const cors = require("cors"); app.use(cors());

3️⃣ uuid — Unique IDs
Instead of inventing IDs:
const { v4: uuid } = require("uuid"); const user = { id: uuid(), name: "John" };
Every new resource gets a unique identifier.

4️⃣ dotenv — Environment Variables
Instead of writing this in code:
const PORT = 3000;
Put it in .env:
PORT=3000 DATABASE_URL=...
Load it:
require("dotenv").config();
Use it:
app.listen(process.env.PORT);

5️⃣ nodemon — Auto restart server ❤️
When you save file → server restarts automatically.
Install:
npm install -g nodemon
Run:
nodemon app.js
This saves hours of pain.

📚 Documentation

📘 Express Router: https://expressjs.com/en/guide/routing.html
📘 Morgan: https://www.npmjs.com/package/morgan
📘 CORS: https://www.npmjs.com/package/cors

💥Week 7 Day 7 challenges

🧩 Challenge 1: Modular Blog API

👉 Build a small blog API using Express Router.
Requirements:
Create routes folder
🗂️ posts.js
🗂️ authors.js
Each file should export a router
Main app.js must use them like:
app.use("/posts", postsRouter); app.use("/authors", authorsRouter);
Endpoints to include (just dummy responses):
✔ /posts/ → return list of posts
✔ /posts/:id → return a single post
✔ /authors/ → return list of authors
✔ /authors/:id → return author details
Add middleware:
Use morgan for request logging
Use uuid to generate post IDs

🧩 Challenge 2: Notes API with Router + File Storage

👉 Build a simple Notes API, split into modules:
📁 /routes/notes.js
📁 /data/notes.json
Endpoints:
✔ GET /notes → return all notes
✔ POST /notes → add a new note
✔ DELETE /notes/:id → delete a note
Requirements:
➙Use uuid to generate IDs
➙Use fs to read/write JSON file
➙Use express.json()` middleware
Extra:
Add CORS package so any frontend can access it

🧩 Challenge 3: Student Manager

👉 Create Student Manager with:
📁 /routes/students.js
📁 /data/students.json
Endpoints:
✔ GET /students
✔ POST /students
✔ GET /students/:id
✔ DELETE /students/:id
Use packages:
dotenv → load PORT from .env
nodemon → auto restart
.env example:
PORT=4000

🎁 Optional Bonus
Add routes with Router-level middleware:
Example:
router.use((req, res, next) => {
  console.log("Students Router  middleware running");
next(); });

When you are done:
💥share your solutions in the group,
💥invite a friend,
      and as always —

💥stay well, stay curious, and stay coding ✌️

Express review questions