Express Basics

Q: Is Express 5 production-ready?

Yes on Node 24 LTS. It is the current npm latest major. Migrate from Express 4 using the official migration guide patterns in Express 5 Migration.

Q: Should I use app.listen or http.createServer?

app.listen is fine for most apps. Use createServer(app) when you need direct access to the underlying server for WebSocket upgrades or timeout tuning.

Q: How do I structure a large Express app?

Routers per domain (/users, /orders), services for business logic, separate app.ts and server.ts. See Express Best Practices.

Q: Does Express support ESM?

Yes. Set "type": "module" in package.json and use import express from "express".

10 examples to build your first Express 5 API - 7 basic and 3 intermediate.

Prerequisites

mkdir express-api && cd express-api
npm init -y
npm pkg set type=module
npm install express@5
npm install -D typescript@5.6 tsx @types/express @types/node

For middleware ordering and security hardening, see Middleware Ordering and Security Middleware.

Basic Examples

1. Hello World Server

import express from "express";
 
const app = express();
const port = 3000;
 
app.get("/", (_req, res) => {
  res.send("Hello from Express 5\n");
});
 
app.listen(port, () => {
  console.log(`http://localhost:${port}`);
});

app is a function that wraps Node's http.createServer
res.send() sets Content-Type automatically based on the payload
Express 5 requires Node 18+; use Node 24 LTS in production

2. JSON Body Parsing

import express from "express";
 
const app = express();
app.use(express.json({ limit: "1mb" }));
 
app.post("/users", (req, res) => {
  const { name, email } = req.body;
  res.status(201).json({ id: 1, name, email });
});

express.json() must be registered before routes that read req.body
Set limit to prevent large payload attacks
Fastify includes JSON parsing by default with schema validation

3. Route Parameters

import express from "express";
 
const app = express();
 
app.get("/users/:id", (req, res) => {
  const { id } = req.params;
  res.json({ id, name: "Ada Lovelace" });
});

req.params contains named route segments
Express 5 changed wildcard routing syntax - see Express 5 Migration
Validate id format in the handler or a validation middleware

4. Query Strings

import express from "express";
 
const app = express();
 
app.get("/search", (req, res) => {
  const q = req.query.q as string | undefined;
  const page = Number(req.query.page ?? 1);
  res.json({ q, page, results: [] });
});

req.query is parsed automatically
Cast query values in TypeScript; they arrive as strings or arrays
Use a validation library (Zod) at the boundary for production APIs

5. Router for Modular Routes

import express, { Router } from "express";
 
const app = express();
const usersRouter = Router();
 
usersRouter.get("/", (_req, res) => {
  res.json([{ id: 1, name: "Ada" }]);
});
 
usersRouter.get("/:id", (req, res) => {
  res.json({ id: req.params.id });
});
 
app.use("/users", usersRouter);

Router is a mini-app with its own middleware stack
Mount routers at path prefixes to organize large APIs
NestJS modules serve a similar grouping purpose with DI

6. Middleware for Request Logging

import express from "express";
 
const app = express();
 
app.use((req, _res, next) => {
  console.log(`${req.method} ${req.url}`);
  next();
});
 
app.get("/health", (_req, res) => {
  res.json({ status: "ok" });
});

Middleware runs in registration order
Call next() to pass control to the next handler
See Middleware Pattern for the underlying pattern

7. Static File Serving

import express from "express";
import { join } from "node:path";
 
const app = express();
 
app.use("/static", express.static(join(import.meta.dirname, "public")));

express.static serves files from a directory
Place static middleware before API routes or use a dedicated path prefix
In production, nginx or a CDN usually serves static assets instead

Intermediate Examples

8. Async Route Handlers (Express 5)

import express from "express";
 
const app = express();
 
app.get("/users/:id", async (req, res) => {
  const user = await findUser(req.params.id);
  if (!user) {
    res.status(404).json({ error: "Not found" });
    return;
  }
  res.json(user);
});
 
async function findUser(id: string) {
  if (id === "999") return null;
  return { id, name: "Ada" };
}

Express 5 forwards rejected promises to error middleware automatically
Express 4 required express-async-errors or manual try/catch wrappers
Always return after sending error responses to avoid double-send

9. Error Middleware

import express, { type Request, type Response, type NextFunction } from "express";
 
const app = express();
 
app.get("/fail", () => {
  throw new Error("Something broke");
});
 
app.use((err: Error, _req: Request, res: Response, _next: NextFunction) => {
  console.error(err);
  res.status(500).json({ error: "Internal server error" });
});

Error middleware has 4 parameters: (err, req, res, next)
Register it after all routes
Never expose stack traces to clients in production

10. Environment-Based Configuration

import express from "express";
 
const app = express();
const port = Number(process.env.PORT ?? 3000);
const isDev = process.env.NODE_ENV !== "production";
 
if (isDev) {
  app.use((req, _res, next) => {
    console.log(`[dev] ${req.method} ${req.path}`);
    next();
  });
}
 
app.get("/health", (_req, res) => {
  res.json({ env: process.env.NODE_ENV ?? "development" });
});
 
app.listen(port);

Use PORT from the environment (Heroku, Railway, K8s all set this)
Gate debug middleware behind NODE_ENV
See Configuration Basics for schema validation

FAQs

Is Express 5 production-ready?

Yes on Node 24 LTS. It is the current npm latest major. Migrate from Express 4 using the official migration guide patterns in Express 5 Migration.

Express vs Fastify for a new project?

Express if team familiarity and ecosystem size matter most. Fastify if throughput and JSON schema validation are priorities. See Fastify vs Express ADR.

Should I use `app.listen` or `http.createServer`?

app.listen is fine for most apps. Use createServer(app) when you need direct access to the underlying server for WebSocket upgrades or timeout tuning.

How do I structure a large Express app?

Routers per domain (/users, /orders), services for business logic, separate app.ts and server.ts. See Express Best Practices.

Does Express support ESM?

Yes. Set "type": "module" in package.json and use import express from "express".

Middleware Ordering - registration sequence
Error Handling in Express - async and sync errors
Security Middleware - helmet, cors, rate limits
Fastify Basics - performance alternative
Express Best Practices - section checklist

Express.js - Official Express site and guides.
MDN Web Docs – Express/Node.js - Beginner-to-intermediate Express/Node tutorials.
freeCodeCamp – Backend Development & APIs - Free certification path with Node/Express projects.
Node.js in Action, 2nd Edition - Classic practical Node.js.
Get Programming with Node.js - Introductory programming with Node.js.

Stack versions: This page was written for Node.js 24.18.0 (Active LTS), npm 10+, TypeScript 5.6+, Express 5, Fastify 5, and NestJS 11.

Prerequisites

mkdir express-api && cd express-api
npm init -y
npm pkg set type=module
npm install express@5
npm install -D typescript@5.6 tsx @types/express @types/node

For middleware ordering and security hardening, see Middleware Ordering and Security Middleware.

Basic Examples

1. Hello World Server

import express from "express";
 
const app = express();
const port = 3000;
 
app.get("/", (_req, res) => {
  res.send("Hello from Express 5\n");
});
 
app.listen(port, () => {
  console.log(`http://localhost:${port}`);
});

app is a function that wraps Node's http.createServer
res.send() sets Content-Type automatically based on the payload
Express 5 requires Node 18+; use Node 24 LTS in production

2. JSON Body Parsing

import express from "express";
 
const app = express();
app.use(express.json({ limit: "1mb" }));
 
app.post("/users", (req, res) => {
  const { name, email } = req.body;
  res.status(201).json({ id: 1, name, email });
});

express.json() must be registered before routes that read req.body
Set limit to prevent large payload attacks
Fastify includes JSON parsing by default with schema validation

3. Route Parameters

import express from "express";
 
const app = express();
 
app.get("/users/:id", (req, res) => {
  const { id } = req.params;
  res.json({ id, name: "Ada Lovelace" });
});

req.params contains named route segments
Express 5 changed wildcard routing syntax - see Express 5 Migration
Validate id format in the handler or a validation middleware

4. Query Strings

import express from "express";
 
const app = express();
 
app.get("/search", (req, res) => {
  const q = req.query.q as string | undefined;
  const page = Number(req.query.page ?? 1);
  res.json({ q, page, results: [] });
});

req.query is parsed automatically
Cast query values in TypeScript; they arrive as strings or arrays
Use a validation library (Zod) at the boundary for production APIs

5. Router for Modular Routes

import express, { Router } from "express";
 
const app = express();
const usersRouter = Router();
 
usersRouter.get("/", (_req, res) => {
  res.json([{ id: 1, name: "Ada" }]);
});
 
usersRouter.get("/:id", (req, res) => {
  res.json({ id: req.params.id });
});
 
app.use("/users", usersRouter);

Router is a mini-app with its own middleware stack
Mount routers at path prefixes to organize large APIs
NestJS modules serve a similar grouping purpose with DI

6. Middleware for Request Logging

import express from "express";
 
const app = express();
 
app.use((req, _res, next) => {
  console.log(`${req.method} ${req.url}`);
  next();
});
 
app.get("/health", (_req, res) => {
  res.json({ status: "ok" });
});

Middleware runs in registration order
Call next() to pass control to the next handler
See Middleware Pattern for the underlying pattern

7. Static File Serving

import express from "express";
import { join } from "node:path";
 
const app = express();
 
app.use("/static", express.static(join(import.meta.dirname, "public")));

express.static serves files from a directory
Place static middleware before API routes or use a dedicated path prefix
In production, nginx or a CDN usually serves static assets instead

Intermediate Examples

8. Async Route Handlers (Express 5)

import express from "express";
 
const app = express();
 
app.get("/users/:id", async (req, res) => {
  const user = await findUser(req.params.id);
  if (!user) {
    res.status(404).json({ error: "Not found" });
    return;
  }
  res.json(user);
});
 
async function findUser(id: string) {
  if (id === "999") return null;
  return { id, name: "Ada" };
}

Express 5 forwards rejected promises to error middleware automatically
Express 4 required express-async-errors or manual try/catch wrappers
Always return after sending error responses to avoid double-send

9. Error Middleware

import express, { type Request, type Response, type NextFunction } from "express";
 
const app = express();
 
app.get("/fail", () => {
  throw new Error("Something broke");
});
 
app.use((err: Error, _req: Request, res: Response, _next: NextFunction) => {
  console.error(err);
  res.status(500).json({ error: "Internal server error" });
});

Error middleware has 4 parameters: (err, req, res, next)
Register it after all routes
Never expose stack traces to clients in production

10. Environment-Based Configuration

import express from "express";
 
const app = express();
const port = Number(process.env.PORT ?? 3000);
const isDev = process.env.NODE_ENV !== "production";
 
if (isDev) {
  app.use((req, _res, next) => {
    console.log(`[dev] ${req.method} ${req.path}`);
    next();
  });
}
 
app.get("/health", (_req, res) => {
  res.json({ env: process.env.NODE_ENV ?? "development" });
});
 
app.listen(port);

Use PORT from the environment (Heroku, Railway, K8s all set this)
Gate debug middleware behind NODE_ENV
See Configuration Basics for schema validation

FAQs

Is Express 5 production-ready?

Yes on Node 24 LTS. It is the current npm latest major. Migrate from Express 4 using the official migration guide patterns in Express 5 Migration.

Express vs Fastify for a new project?

Express if team familiarity and ecosystem size matter most. Fastify if throughput and JSON schema validation are priorities. See Fastify vs Express ADR.

Should I use `app.listen` or `http.createServer`?

app.listen is fine for most apps. Use createServer(app) when you need direct access to the underlying server for WebSocket upgrades or timeout tuning.

How do I structure a large Express app?

Routers per domain (/users, /orders), services for business logic, separate app.ts and server.ts. See Express Best Practices.

Does Express support ESM?

Yes. Set "type": "module" in package.json and use import express from "express".

Middleware Ordering - registration sequence
Error Handling in Express - async and sync errors
Security Middleware - helmet, cors, rate limits
Fastify Basics - performance alternative
Express Best Practices - section checklist

Express.js - Official Express site and guides.
MDN Web Docs – Express/Node.js - Beginner-to-intermediate Express/Node tutorials.
freeCodeCamp – Backend Development & APIs - Free certification path with Node/Express projects.
Node.js in Action, 2nd Edition - Classic practical Node.js.
Get Programming with Node.js - Introductory programming with Node.js.

Stack versions: This page was written for Node.js 24.18.0 (Active LTS), npm 10+, TypeScript 5.6+, Express 5, Fastify 5, and NestJS 11.

Express Basics

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Express Basics