express

Express

Express is a minimalist, unopinionated web framework for Node.js, providing robust HTTP utility methods, extensible middleware architectures, and async handler support.

When to Use

• Fast Node.js REST API Development: Building flexible, lightweight HTTP microservices and web backends.
• Established Node.js Ecosystem Services: Leveraging thousands of battle-tested npm middleware packages.
• Web App Routing & Server-Side Rendering: Serving dynamic server-side templates with EJS, Pug, or Handlebars.
• API Gateways & Proxy Layers: Routing, inspecting, and transforming inbound microservice requests.

Quick Start

import express from "express";
const app = express();

// Express 5 handles async errors automatically!
app.get("/", async (req, res) => {
  const user = await db.getUser(); // If this throws, Express catches it.
  res.json(user);
});

app.listen(3000);

Core Concepts

Modular Route Handlers & Express Router

Structuring scalable APIs with decoupled sub-routers:

import express, { Request, Response, NextFunction } from "express";

const userRouter = express.Router();

interface UserPayload {
  username: string;
  email: string;
}

userRouter.get(
  "/:id",
  async (req: Request, res: Response, next: NextFunction) => {
    try {
      const userId = req.params.id;
      res.json({ id: userId, username: `user_${userId}`, status: "active" });
    } catch (error) {
      next(error);
    }
  },
);

userRouter.post(
  "/",
  async (
    req: Request<{}, {}, UserPayload>,
    res: Response,
    next: NextFunction,
  ) => {
    try {
      const { username, email } = req.body;
      if (!username || !email) {
        res.status(400).json({ error: "Username and email are required" });
        return;
      }
      res.status(201).json({ id: Date.now(), username, email });
    } catch (error) {
      next(error);
    }
  },
);

export default userRouter;

Custom Middleware & Security Pipeline