MEAN Stack Last-Minute Revision

30 quick revision notes for MEAN Stack

1. TypeScript adds static types to JavaScript; prefer unknown over any for untrusted data and narrow it before use.
2. Interfaces can merge and extend, while type aliases also describe unions, tuples and mapped types.
3. Partial, Pick, Omit and Record transform existing types, which keeps API request and response models consistent.
4. An Observable is lazy, can emit many values and can be cancelled, while a Promise is eager and resolves once.
5. Standalone components are the default in modern Angular and declare their dependencies in their own imports array.
6. Built-in control flow uses @if, @for with a required track expression, and @switch instead of structural directives.
7. Use input(), output() and model() for component communication, and viewChild to access a child component directly.
8. OnPush change detection checks a component only on new input references, its own events, async pipe or signal changes.
9. Zoneless change detection removes Zone.js and relies on signals, template events and markForCheck to schedule updates.
10. @defer lazy loads part of a template with triggers such as on viewport, on interaction or on idle.
11. providedIn root creates a single tree-shakable service instance shared across the whole application.
12. The inject() function works in field initialisers, functional guards, resolvers and interceptors inside an injection context.
13. InjectionToken lets you provide non-class values such as configuration objects or API base URLs.
14. canMatch prevents a lazy route from matching at all, so unauthorised users never download that feature's code.
15. canDeactivate guards protect users from losing unsaved form data when navigating away.
16. A signal is read by calling it, computed derives memoised values, and effect runs side effects when dependencies change.
17. switchMap cancels the previous inner request, concatMap queues, mergeMap runs in parallel and exhaustMap ignores new triggers.
18. BehaviorSubject needs an initial value and replays the latest value to every new subscriber.
19. Use the async pipe, toSignal or takeUntilDestroyed to avoid subscription memory leaks in components.
20. Typed reactive forms use FormGroup, FormControl and FormArray, and NonNullableFormBuilder resets to initial values.
21. Cross-field validation such as password confirmation belongs on the FormGroup, not on a single control.
22. Functional HTTP interceptors registered with withInterceptors attach tokens, handle errors and refresh expired sessions.
23. Synchronous CPU-heavy work in an Express handler blocks the Node.js event loop and slows every other request.
24. Always validate request bodies on the server, because clients can bypass Angular validation by calling the API directly.
25. Serve the Angular build with a fallback to index.html so deep links do not return 404 after refresh.
26. Use atomic MongoDB updates with $inc and conditions to avoid lost updates in balances and stock counts.
27. TTL indexes automatically delete documents such as OTPs or sessions after a configured number of seconds.
28. Angular sanitises interpolated and bound values to prevent XSS; bypassSecurityTrust methods should be used only for trusted content.
29. Test HTTP services with provideHttpClientTesting and HttpTestingController, flushing fake responses and verifying no extra calls.
30. Angular SSR renders HTML on the server and hydration attaches the app in the browser, improving SEO and first load.

Night-before checklist

• Revise your saved questions on this page once, aloud.
• Read the quick notes and mark any you cannot explain in one line.
• Rehearse a two-minute self-introduction and two project stories.
• Keep CV, ID, laptop charger and interview link ready; sleep on time.