Express 5 Cheatsheet

Setup

• Install Express — Add Express to a Node.js project.
• Hello world server — The smallest Express app. It listens on port 3000.
• Run with auto-restart — Restart the server when files change, using Node's built-in watcher.
• Load environment variables — Read PORT and other settings from a .env file.

Routing

• Read a route parameter — Capture part of the URL as a parameter.
• Read the query string — Read values such as ?page=2.
• Handle a JSON body — Parse JSON request bodies, then read req.body.
• Group routes in a router — Put related routes in a router and mount it under a prefix.
• Send a status and JSON — Set the status code and send a JSON response.
• Redirect — Redirect the client to another URL.

Middleware

• Write middleware — Run code on every request, then call next() to continue.
• Serve static files — Serve files from the public folder.
• Enable CORS — Allow browsers on other origins to call your API.
• Set security headers — Add common protective HTTP headers.
• Log requests — Log each request with the morgan middleware.
• Trust a reverse proxy — Read the client's real IP and protocol behind a proxy such as Nginx.

Error handling

• Handle errors in async routes — In Express 5, a rejected promise or thrown error in an async handler is passed to the error handler automatically.
• Add an error handler — Define it last. It takes four arguments.
• Handle 404s — Add a catch-all after your routes.

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