#Express.js Backend Template

A template for building a backend application using Node.js and Express.js.

---

#Project Setup

bashcopymkdir my-app
cd my-app
npm init -y
npm install express cors
npm install --save-dev nodemon

Update package.json to add a dev script:

jsoncopy{
  "scripts": {
    "start": "node index.js",
    "dev": "nodemon index.js"
  }
}

---

#Basic Server Structure

jscopyconst express = require("express");
const cors = require("cors");
const app = express();
const PORT = 3000;

// Middleware
app.use(express.json());
app.use(cors());

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

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

---

#CORS Configuration

#Allow All Origins (Development)

jscopyapp.use(cors());

#Restricted Origins (Production)

jscopyapp.use(
  cors({
    origin: "http://localhost:5173", // e.g. Vite / React frontend
    methods: ["GET", "POST", "PUT", "DELETE"],
    allowedHeaders: ["Content-Type", "Authorization"],
  })
);

#Separate CORS Middleware File (middleware/cors.js)

jscopyconst cors = require("cors");

const corsOptions = {
  origin: process.env.CLIENT_URL || "http://localhost:5173",
  methods: ["GET", "POST", "PUT", "DELETE"],
  allowedHeaders: ["Content-Type", "Authorization"],
};

module.exports = cors(corsOptions);

Register in index.js:

jscopyconst corsMiddleware = require("./middleware/cors");
app.use(corsMiddleware);

Without CORS, the browser will block requests from a frontend running on
a different port — e.g. React/Vite on 5173 → Express on 3000.

---

#Routing

#Inline Routes

jscopyapp.get("/users", (req, res) => {
  res.json({ users: [] });
});

app.post("/users", (req, res) => {
  const { name, email } = req.body;
  res.status(201).json({ message: "User created", name, email });
});

app.put("/users/:id", (req, res) => {
  const { id } = req.params;
  res.json({ message: `User ${id} updated` });
});

app.delete("/users/:id", (req, res) => {
  const { id } = req.params;
  res.json({ message: `User ${id} deleted` });
});

#Separate Router File (routes/users.js)

jscopyconst express = require("express");
const router = express.Router();

router.get("/", (req, res) => {
  res.json({ users: [] });
});

router.post("/", (req, res) => {
  const { name, email } = req.body;
  res.status(201).json({ message: "User created", name, email });
});

module.exports = router;

Register the router in index.js:

jscopyconst userRoutes = require("./routes/users");
app.use("/users", userRoutes);

---

#URL Parameters & Query Strings

jscopy// URL param: GET /users/42
app.get("/users/:id", (req, res) => {
  const { id } = req.params;
  res.json({ userId: id });
});

// Query string: GET /search?name=John&age=25
app.get("/search", (req, res) => {
  const { name, age } = req.query;
  res.json({ name, age });
});

---

#Middleware

jscopy// Global logging middleware
app.use((req, res, next) => {
  console.log(`[${new Date().toISOString()}] ${req.method} ${req.url}`);
  next();
});

// Route-specific middleware
function isAuthenticated(req, res, next) {
  const token = req.headers["authorization"];
  if (!token) return res.status(401).json({ error: "Unauthorized" });
  next();
}

app.get("/protected", isAuthenticated, (req, res) => {
  res.json({ message: "Access granted" });
});

---

#Project Structure (Recommended)

textcopymy-app/
├── routes/
│   └── users.js
├── controllers/
│   └── userController.js
├── middleware/
│   ├── auth.js
│   └── cors.js
├── index.js
└── package.json