Introduction to Express

Express.js is a minimal, unopinionated web framework for Node.js. Instead of forcing you into one way of building an app, it hands you a small toolkit — routing, middleware, and request/ response helpers — and lets you organize the rest however you like.

• Middleware-driven: almost everything in Express, from parsing a request body to logging, happens through middleware functions chained together.
• Flexible routing: you decide how routes, controllers, and folders are laid out.
• Plays well with others: pairs easily with MongoDB, PostgreSQL, MySQL, or any front-end framework.
• Scales down and up: fine for a weekend script, fine for a production API.

A tiny Express app

const express = require("express");
const app = express();
const PORT = 4000;

app.get("/", (req, res) => {
    res.send("Task Manager API is running");
});

app.listen(PORT, () => {
    console.log(`Server listening at http://localhost:${PORT}`);
});

Run it with node server.js, then open http://localhost:4000 in a browser — you'll see "Task Manager API is running".

What happens under the hood

1. A client (browser, mobile app, curl) sends a request to the server.
2. The request passes through any middleware registered before the matching route — this is where logging, authentication, or body parsing usually happens.
3. Express looks at the URL and HTTP verb and finds the matching route handler.
4. The handler builds a response and hands it back.
5. The response travels back to the client.
6. If something throws along the way, error-handling middleware catches it so the server doesn't crash.

Why teams reach for Express

Express became the default choice for Node backends because it removes a lot of repetitive plumbing:

• Routing — map a URL and HTTP verb to a function.

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

• Middleware — functions that can inspect or modify req/res before the final handler runs.

app.use((req, res, next) => {
    console.log(`${req.method} ${req.url} at ${new Date().toISOString()}`);
    next();
});

• Error handling — a special four-argument middleware catches errors thrown anywhere in the chain.

app.use((err, req, res, next) => {
    console.error(err.stack);
    res.status(500).send("Something broke on our end");
});

Where Express is typically used

• Traditional server-rendered web apps and SPA backends
• REST APIs for CRUD-style resources
• Lightweight microservices
• Server-side rendering with template engines
• Reverse proxies / API gateways
• Rapid prototypes and internal tools