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Lessons (8)

• Behavioral Patterns II: Chain, Template, Iterator, Mediator, Memento, Visitor

  Six more behavioral patterns, from Express-style middleware chains to undo snapshots, each with a picture and a …

• O — Open/Closed Principle

  … StudentDiscount : 🆕 added later OCP is everywhere you look Tool Extension point --- --- Express / Koa Middleware: app.use(myMiddleware) VS …

• Which Pattern Do I Need?

  … 2. 🔌 Adapter — wrapping 3rd-party libraries 3. ☕ Decorator — middleware, HOCs, retry/cache/log wrappers 4. 🏨 Facade — service layers …

• How a Web Request Works

  … through layers: mermaid flowchart LR R[Request] -- M["Middleware<br/ logging, auth, rate limit"] -- Rt[Router] -- C[Controller …

• What Are Design Patterns?

  … pattern --- --- button.addEventListener("click", fn) Observer app.use(middleware) in Express Chain of Responsibility array.sort((a, b …

• Clean Error Handling

  … Throw specific errors, and let one middleware turn them into HTTP responses. js // routes just throw app.get …

• State Management (Redux, Zustand, TanStack Query)

  … strict conventions, excellent DevTools (time-travel debugging) and middleware. RTK Query adds server-state caching, similar to TanStack …

• Structural Patterns: How to Connect Objects

  … withRetry] -- F[fetchUser] You've used it: Express middleware, React Higher-Order Components ( withRouter(Component) ), TypeScript/NestJS @decorators …