Express.js Cheat Sheet

Updated 2026-04-28

Express.js is a minimal and flexible Node.js web application framework that provides a robust set of features for building web and mobile applications. It sits atop Node.js as a de facto standard server framework for REST APIs, web applications, and microservices. Express 5 (released October 2024) modernizes the framework by requiring Node.js 18+, automatically forwarding rejected promises to error handlers, tightening route-pattern security via path-to-regexp v8, and adding native Brotli compression support. Understanding middleware execution order, asynchronous error handling patterns, and the request-response lifecycle is essential for leveraging Express effectively in production.

What This Cheat Sheet Covers

This topic spans 28 focused tables and 197 indexed concepts. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.

Table 1: Core Application MethodsTable 2: HTTP Route MethodsTable 3: Routing and Path MatchingTable 4: Router for Modular RoutingTable 5: Middleware TypesTable 6: Request Object PropertiesTable 7: Response Object MethodsTable 8: Body ParsingTable 9: Static File ServingTable 10: Template EnginesTable 11: Error HandlingTable 12: Validation and SanitizationTable 13: Security MiddlewareTable 14: Session and AuthenticationTable 15: File Upload HandlingTable 16: LoggingTable 17: Performance OptimizationTable 18: TestingTable 19: Environment ConfigurationTable 20: Database Integration PatternsTable 21: Real-Time CommunicationTable 22: GraphQL IntegrationTable 23: API VersioningTable 24: Express 5 Migration ChangesTable 25: TypeScript IntegrationTable 26: Health Checks and Graceful ShutdownTable 27: OpenAPI/Swagger DocumentationTable 28: Background Job Processing

Table 1: Core Application Methods

Method	Example	Description
app.listen()	`app.listen(3000, () => console.log('Server running'))`	Starts the Express application and binds it to a specified port, listening for incoming HTTP requests.
app.use()	`app.use(express.json())` `app.use('/api', routes)`	• Mounts middleware functions at a specified path • executes for every request matching that path, or globally if no path specified.
app.set()	`app.set('view engine', 'ejs')` `app.set('port', 3000)`	• Assigns a configuration setting to a name • used for application-level settings like template engine or custom properties.
app.get() (setting)	`const port = app.get('port')`	Retrieves the value of a setting previously assigned with `app.set()`.
app.locals	`app.locals.title = 'My App'`	Object containing application-level variables accessible throughout the app's lifecycle, including inside templates.

Table 1: Core Application Methods

Method	Example	Description
app.listen()	`app.listen(3000, () => console.log('Server running'))`	Starts the Express application and binds it to a specified port, listening for incoming HTTP requests.
app.use()	`app.use(express.json())` `app.use('/api', routes)`	• Mounts middleware functions at a specified path • executes for every request matching that path, or globally if no path specified.
app.set()	`app.set('view engine', 'ejs')` `app.set('port', 3000)`	• Assigns a configuration setting to a name • used for application-level settings like template engine or custom properties.
app.get() (setting)	`const port = app.get('port')`	Retrieves the value of a setting previously assigned with `app.set()`.
app.locals	`app.locals.title = 'My App'`	Object containing application-level variables accessible throughout the app's lifecycle, including inside templates.