Express.js Cheat Sheet

A single-page, comprehensive reference for the Express.js APIs, methods, and patterns covered throughout this course. Bookmark this page for quick lookups while building real applications.

How to Use This Cheat Sheet

Each table below groups a related set of Express APIs or conventions, application methods, routing, middleware types, request/response members, common third-party packages, and HTTP status codes, so you can jump straight to what you need.

const express = require('express');
const app = express();

app.use(express.json());
app.get('/users/:id', (req, res) => res.json({ id: req.params.id }));
app.listen(3000);

The five lines above touch nearly every category covered in the tables below: app creation, middleware, routing, parameters, and starting the server.

Quick Project Bootstrap

mkdir my-app && cd my-app
npm init -y
npm install express dotenv
npm install -D nodemon

This is the fastest path from an empty folder to a runnable Express project.
Add helmet, cors, and express-rate-limit immediately for any public-facing API.
Add express-validator or Joi as soon as routes accept client input.

Application Methods

Core methods on the app object.

Method	Purpose
`app.set(name, value)`	Store an app-wide setting
`app.get(name)`	Read an app-wide setting
`app.use([path], fn)`	Register middleware
`app.METHOD(path, fn)`	Register a route for a given HTTP method
`app.route(path)`	Chain multiple methods on one path
`app.listen(port, cb)`	Start the HTTP server
`app.locals`	Data shared across the app's lifetime

Routing Reference

The HTTP methods and path patterns you will use to define routes.

Pattern	Example
Exact path	`app.get('/about', fn)`
Route parameter	`app.get('/users/:id', fn)`
Multiple parameters	`app.get('/users/:userId/posts/:postId', fn)`
Optional parameter	`app.get('/products/:id?', fn)`
Any method	`app.all('/status', fn)`

Middleware Reference

Built-in and commonly installed middleware.

Middleware	Purpose
`express.json()`	Parse JSON request bodies
`express.urlencoded({ extended: true })`	Parse form-encoded bodies
`express.static(dir)`	Serve static files
`cors()`	Enable Cross-Origin Resource Sharing
`helmet()`	Set secure HTTP headers
`morgan('dev')`	Log HTTP requests
`express-rate-limit`	Limit requests per client
`multer()`	Handle multipart file uploads
`cookie-parser`	Parse cookies into `req.cookies`
`express-session`	Manage server-side sessions

req / res Reference

The most-used properties and methods on the request and response objects.

Member	Description
`req.params`	Named route segment values
`req.query`	Query string values
`req.body`	Parsed request body
`req.headers`	Request headers
`req.get(name)`	Read a single request header
`res.status(code)`	Set the response status code
`res.json(obj)`	Send a JSON response
`res.send(body)`	Send a text/HTML response
`res.redirect(url)`	Redirect the client
`res.cookie(name, value, opts)`	Set a cookie

HTTP Status Code Reference

The status codes you'll use in almost every REST API.

Code	Meaning	Typical Use
200	OK	Successful GET/PUT/PATCH
201	Created	Successful POST that created a resource
204	No Content	Successful DELETE with no response body
400	Bad Request	Validation failure
401	Unauthorized	Missing or invalid authentication
403	Forbidden	Authenticated but not permitted
404	Not Found	Resource does not exist
409	Conflict	Duplicate or conflicting resource
429	Too Many Requests	Rate limit exceeded
500	Internal Server Error	Unexpected server-side error

Common Mistakes

Bookmarking a cheat sheet but never revisiting the deeper lessons behind each entry.
Copying a pattern from a table without understanding when it does or doesn't apply.
Skipping the security-related middleware rows when starting a new public-facing project.

Key Takeaways

This cheat sheet condenses the application, routing, middleware, req/res, and status code APIs covered throughout the course.
Use it as a quick lookup while building, not as a replacement for understanding the underlying concepts.
Security middleware (helmet, cors, rate limiting) belongs in nearly every production Express project.

Pro Tip

Keep this cheat sheet open in a browser tab while building your first few Express projects, over time you'll find yourself needing it less and less as the patterns become second nature.