Home›Express.js in 5 Days›Day 1
Day 1 of 5
⏱ ~60 minutes
Express.js in 5 Days — Day 1

Routes and Middleware

Set up an Express server, define routes for all HTTP methods, write middleware, and understand the request/response cycle.

Your First Express Server

Terminal
mkdir my-api && cd my-api
npm init -y
npm install express
npm install -D nodemon
server.js
const express = require('express');
const app = express();
const PORT = process.env.PORT || 3000;

// Built-in middleware: parse JSON bodies
app.use(express.json());
app.use(express.urlencoded({ extended: true }));

// Routes
app.get('/', (req, res) => {
  res.json({ message: 'API is running' });
});

app.get('/users/:id', (req, res) => {
  const { id } = req.params;           // route params
  const { page = 1 } = req.query;     // query string
  res.json({ id, page });
});

app.post('/users', (req, res) => {
  const { name, email } = req.body;   // JSON body
  // save to DB...
  res.status(201).json({ name, email });
});

app.listen(PORT, () => console.log(`Server on port ${PORT}`));
Custom Middleware
// Middleware: runs before route handlers
// Must call next() or the request hangs

// Request logger
app.use((req, res, next) => {
  console.log(`${req.method} ${req.path} ${new Date().toISOString()}`);
  next();
});

// Route-specific middleware
function requireApiKey(req, res, next) {
  const key = req.headers['x-api-key'];
  if (key !== process.env.API_KEY) {
    return res.status(401).json({ error: 'Unauthorized' });
  }
  next();
}

app.get('/secure', requireApiKey, (req, res) => {
  res.json({ secret: 'data' });
});
💡
Middleware order matters. Middleware defined with app.use() runs in order for every request. Put your logger first, auth middleware before protected routes, error handlers last.
📝 Day 1 Exercise
Build a REST API Skeleton
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Day 1 Summary

  • Express is a thin layer over Node's HTTP module. app.use() adds middleware. app.get/post/put/delete() adds routes.
  • Middleware signature: (req, res, next). Call next() to pass to the next handler.
  • req.params = route params. req.query = query string. req.body = parsed body (needs middleware).
  • res.json(data) sends JSON. res.status(201).json(data) sets the status code.
Next →
Day 2: MongoDB and Mongoose
→
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