Express

Express

Express is the standard web framework for Node.js. Express 5 (2025) finally stabilizes modern features like Promise support in middleware, removing the need for express-async-errors.

When to Use

• Microservices: Lightweight and fast.
• REST APIs: The standard for building JSON APIs in Node.
• Learning: The best way to learn how HTTP works in Node.

Quick Start (Express 5)

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

Middleware

Functions that have access to req, res, and next. They form a pipeline. Log -> Auth -> BodyParse -> RouteHandler.

Routing

app.get(), app.post(). Simple regex-based routing.

Best Practices (2025)

Do:

• Upgrade to Express 5: Native Promise support is a game changer for cleaner code.
• Use helmet: Security headers are mandatory.
• Structure properly: Don't put everything in app.js. Use express.Router().

Don't:

• Don't stick to CommonJS: Express 5 supports ESM. Use import.
• Don't use body-parser separate package: Use express.json() (included since v4, standard in v5).

References

• Express 5 Migration Guide

Source: G1Joshi/Agent-Skills — distributed by TomeVault.