Express v5

Minimal web framework for Node.js. v5 is a major rewrite with async error handling, removed deprecated APIs, and modern JS support.

Source: github.com/expressjs/express · npm Version in project: 5.2.1 · Published: 2025-03 · Skill updated: 2026-03-21

When to Use

• Building or modifying HTTP server routes and middleware
• Migrating from Express v4 to v5
• Adding error handling, body parsing, or CORS to an Express app

When NOT to Use

• Working with Telegraf bot webhooks only (use telegraf-v4 skill)
• Building a frontend app — Express is backend only

Installation

npm install express@5
npm install @types/express -D

Basic Server

import express from "express";

const app = express();

app.use(express.json());
app.use(express.urlencoded({ extended: true }));

app.get("/", (req, res) => {
  res.json({ status: "ok" });
});

app.listen(3000, () => {
  console.log("Server running on :3000");
});

Key Differences from v4

✅ Async error handling (automatic)

// v4 — needed try/catch + next(err)
app.get("/data", async (req, res, next) => {
  try {
    const data = await fetchData();
    res.json(data);
  } catch (err) {
    next(err);
  }
});

// v5 — thrown/rejected errors caught automatically
app.get("/data", async (req, res) => {
  const data = await fetchData(); // if this throws, Express catches it
  res.json(data);
});

❌ Removed APIs

Path syntax changes

// v4: optional params with ?
app.get("/user/:id?", handler);

// v5: use {param} syntax for optional
app.get("/user{/:id}", handler);

// v5: regexp in path uses {regexp} syntax
app.get("/file/:name{.:ext}", handler);

Middleware Pattern

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

// Error handler — must have 4 params
app.use((err: Error, req: Request, res: Response, next: NextFunction) => {
  console.error(err.stack);
  res.status(500).json({ error: err.message });
});

Router

import { Router } from "express";


const router = Router();

router.get("/", (req, res) => { ... });
router.post("/", (req, res) => { ... });

export default router;

// Mount in app
app.use("/api/users", userRouter);

Common Middleware

// Body parsing (built-in)
app.use(express.json({ limit: "1kb" }));
app.use(express.urlencoded({ extended: true }));

// CORS
import cors from "cors";
app.use(cors());

// Static files
app.use(express.static("public"));

// Trust proxy (for reverse proxy setups)
app.set("trust proxy", 1);

TypeScript Types

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

// Typed request body/params
type CreateUserBody = { name: string; email: string };

app.post("/users", (req: Request<{}, {}, CreateUserBody>, res: Response) => {
  const { name, email } = req.body;
  res.json({ name, email });
});

⚠️ Gotchas

v5 is NOT v4

Don't copy v4 patterns blindly. Key differences: async errors auto-caught, path syntax changed, some APIs removed. Check the migration guide.

express.json() limit

Default body limit is 100KB. For small payloads, set express.json({ limit: "1kb" }).

Error handler must be 4-param

Express identifies error handlers by having exactly 4 parameters (err, req, res, next). Missing any one makes it a regular middleware.

req.ip with trust proxy

Behind a reverse proxy, req.ip returns the proxy IP. Set app.set("trust proxy", 1) to get the client IP from X-Forwarded-For.