Angular EXPERTISE CHEATSHEET

🔥 Angular Expertise Cheatsheet – One-Liner QnA🔥

Let’s level you up like a Sr. Angular dev preparing for a ₹1CR package or FAANG interview. Pure power moves. Use this like your daily Gita for Angular.

🧠 CORE CONCEPTS

🔹 What is Angular?
A TypeScript-based front-end framework for building SPAs with modular architecture.

🔹 Component vs Module?
Component = UI building block. Module = Logical group of components, directives, pipes, services.

🔹 What is NgModule?
Decorator to define a context for Angular’s injector and compiler—groups components, services, etc.

🔹 What is a Standalone Component?
Component without a module; self-contained with standalone: true – Angular 15+ feature.

🔹 What is a Directive?
Instruction in the DOM – @Directive() creates behavior (e.g. *ngIf, ngClass).

🔹 What is a Pipe?
Transforms data in templates – e.g., {{ date | date:'short' }}.

⚙️ DATA BINDING

🔹 What are the types of data binding?

Interpolation {{}}
Property binding [value]
Event binding (click)
Two-way binding [(ngModel)].

🔹 What is ngModel?
Two-way binding syntax = [value] + (input).

🔁 LIFECYCLE HOOKS

🔹 What’s ngOnInit()?
Fires after the first component render – best for data fetch/setup.

🔹 Order of lifecycle hooks?
ngOnChanges → ngOnInit → ngDoCheck → ngAfterContentInit → ngAfterContentChecked → ngAfterViewInit → ngAfterViewChecked → ngOnDestroy.

🚦 ROUTING

🔹 What is a RouterModule?
It enables routing and navigation between components in Angular apps.

🔹 What is Lazy Loading?
Load feature modules on-demand via route-level loadChildren.

🔹 What’s a Route Guard?
Protects routes using canActivate, canDeactivate, etc. for auth, conditions, etc.

💉 DEPENDENCY INJECTION

🔹 What is DI in Angular?
Automatic service provisioning using Angular’s injector.

🔹 How to register a service?

In @Injectable({ providedIn: 'root' })
In providers[] of a module/component.

🔗 HTTP + OBSERVABLES

🔹 How to make HTTP call?
Use HttpClient.get/post/put/delete() inside a service.

🔹 What is Observable?
RxJS stream to handle async – used by Angular everywhere.

🔹 What is subscribe()?
Triggers execution of an Observable and handles its emissions.

🚨 ERROR HANDLING + FORMS

🔹 Difference: Template vs Reactive Forms?
Template = HTML-driven; Reactive = Code-driven with FormGroup/FormControl.

🔹 How to handle form errors?
Use formControl.errors + formControl.touched in templates.

📦 STATE MANAGEMENT

🔹 What is RxJS?
Reactive programming library – Angular core uses it heavily.

🔹 What is Subject vs BehaviorSubject?
Subject = multicast stream; BehaviorSubject = remembers last value.

🔹 What’s NgRx?
Redux-inspired state management library using Store, Actions, Effects.

⚡ PERFORMANCE & OPTIMIZATION

🔹 How to optimize Angular app?

Lazy load routes
OnPush strategy
Pure pipes
Avoid deep subscriptions
TrackBy in *ngFor.

🔹 What is ChangeDetectionStrategy.OnPush?
Only checks component when inputs change – boosts performance.

🚀 ADVANCED / ARCHITECTURE

🔹 What is Microfrontend (MFE)?
Break Angular app into feature-based apps that load independently at runtime.

🔹 Signals vs Observables?
Signals (Angular 17+) are reactive primitives for state without RxJS overhead.

🔹 Standalone APIs?
No need for NgModules; Components, Pipes, Directives are self-contained.

🔹 SSR vs CSR?
Server-Side Rendering (SSR) boosts SEO/performance by rendering HTML server-side; CSR runs fully in browser.

📁 BEST PRACTICES

🔹 Use feature-based folder structure?
Yes! Keeps code clean and scalable.

🔹 Use trackBy in *ngFor?
Always – prevents re-rendering hell.

🔹 Avoid direct DOM manipulations?
Yes – use Angular Renderer2 or directives.

Let’s go full throttle into Angular — Deep Level One-Liner QnAs
(This round’s for folks gunning for 1CR+ Sr. Angular Architect roles, not beginners stuck at [(ngModel)])

🔥 Angular DEEP DIVE – One-Liner QnAs (Advanced)

⚙️ CHANGE DETECTION & PERFORMANCE

🔹 What triggers Angular’s change detection?
Any async event – setTimeout, HTTP, user input, zone.js patch.

🔹 How does OnPush change detection work?
It only re-renders the component when its @Input() reference changes.

🔹 What is ngZone used for?
To run code inside/outside Angular's change detection zone.

🔹 How to manually trigger change detection?
Use ChangeDetectorRef.detectChanges() or markForCheck() in OnPush.

🔹 When to use trackBy in *ngFor?
When rendering large lists to avoid unnecessary DOM re-renders.

🧬 SIGNALS (Angular 17+)

🔹 What is a signal in Angular?
A reactive primitive that holds a value and notifies consumers when changed.

🔹 How is signal() different from BehaviorSubject?
Signal is synchronous and fine-grained; no need to subscribe() or unsubscribe().

🔹 How to update a signal?
Use .set(newVal) or .update(fn) to modify its value.

🔹 How to compute derived signals?
Use computed(() => ...) to derive new reactive values from existing signals.

🔹 How to react to signal changes?
Use effect(() => {...}) to run side-effects when signals change.

📦 STANDALONE APIs (No NgModules)

🔹 What is standalone: true for?
Marks component/directive/pipe as not requiring an NgModule.

🔹 How to import features in a standalone component?
Use imports: [CommonModule, FormsModule, MyComponent] directly in the component metadata.

🔹 Can routes use standalone components?
Yes – component: MyStandaloneComponent in route configs.

🔐 AUTH + GUARDS + ROUTING

🔹 What’s the best way to protect a route?
Use canActivate or canLoad with AuthGuard + role logic.

🔹 What’s the difference between canActivate and canLoad?
canActivate = controls route access; canLoad = prevents module from even being loaded.

🔹 What is router state snapshot used for?
It captures the route tree at a moment for accessing params or guards.

🔹 How to pass route data to guards?
Use data property in the route config.

🔁 OBSERVABLES + RXJS

🔹 What is the difference: Subject, BehaviorSubject, ReplaySubject, AsyncSubject?

Subject = no initial, no memory
BehaviorSubject = holds latest value
ReplaySubject = replays last N values
AsyncSubject = emits only final value on complete.

🔹 What is a cold vs hot observable?
Cold = starts on subscribe; Hot = already producing values (e.g., Subject).

🔹 What’s switchMap used for?
Cancel previous request and switch to a new one – ideal for search inputs.

🔹 What’s the danger of nested subscribes?
Memory leaks and callback hell – always flatten with operators (mergeMap, concatMap, etc).

🧠 ARCHITECTURE + STRUCTURE

🔹 What is Smart vs Dumb component?
Smart = container (logic, service); Dumb = presentational (pure input/output).

🔹 Why use feature modules?
Scalability, lazy loading, separation of concerns.

🔹 What is Facade pattern in Angular?
Service layer that hides complexity of store, API, or logic.

🔹 What is Multi-provider token?
Allows multiple values for the same injection token using multi: true.

🔄 FORM CONTROL + REACTIVE FORMS

🔹 How to patch only some values in a form?
Use form.patchValue({ key: value }).

🔹 How to reset a form with default values?
form.reset({ field: 'default' }).

🔹 How to listen to value change in form field?
Use formControl.valueChanges.subscribe().

🔹 What’s the purpose of updateOn: 'blur' or 'submit'?
Delays form updates until blur or submit event.

⚡️ SSR + HYDRATION (Angular 17+)

🔹 What is SSR in Angular?
Rendering Angular app on server to improve SEO and load performance.

🔹 What is hydration in Angular?
Reconnects server-rendered DOM with Angular’s client-side runtime.

🔹 What is transfer state API?
Saves API data from server to client, avoids double-fetching on hydration.

💣 CODE SPLITTING + OPTIMIZATION

🔹 How to implement Lazy Loading for a route?
Use loadChildren: () => import('./feature/feature.routes').then(m => m.ROUTES).

🔹 How to avoid memory leaks in Angular?
Unsubscribe manually, use takeUntil, or AsyncPipe where possible.

🔹 What is the purpose of ng-template?
Holds DOM that is rendered conditionally or lazily.

🔹 Difference between ng-container, ng-template, ng-content?

ng-container: No extra DOM, structural logic
ng-template: Template block
ng-content: Content projection.

👨‍💻 DEV TOOLS & CI/CD

🔹 What is Angular CLI --strict mode?
Tightens type checks and best practices for scalable apps.

🔹 What is esbuild in Angular 18+?
Replaces Webpack for faster builds using blazing-fast bundler.

🔹 What tool for Angular CI/CD builds?
Use GitHub Actions, CircleCI, or GitLab CI with Angular CLI commands.

🔥 Angular Deep Expertise – Volume 3: In-Depth One-Liner QnA

🧱 ADVANCED COMPONENT DESIGN

🔹 How to isolate side effects in Angular components?
Use ngOnInit + services + effect() in Signals for separation of concerns.

🔹 Why prefer @Input() with readonly property?
To ensure immutability and protect from unintended side-effects.

🔹 How to handle dynamic component rendering?
Use ViewContainerRef.createComponent() + ComponentFactoryResolver or new createComponent() API in Angular 14+.

🔹 What is ViewChild({ static: true }) vs false?
true initializes before ngOnInit, false after view init.

🧪 TESTING IN ANGULAR

🔹 What is TestBed?
Angular’s test environment for configuring and creating components and services in isolation.

🔹 How to mock service in Angular unit tests?
Use providers: [{ provide: MyService, useClass: MockService }] in TestBed.

🔹 Difference: unit test vs integration test?
Unit = isolated component/service; Integration = combined components/modules together.

🔹 How to test @Input() and @Output()?
Set inputs manually and use fixture.detectChanges(), subscribe to outputs via spies.

💉 INJECTORS + PROVIDERS

🔹 What is @Self() in DI?
Injects from the local injector only – fails if not found there.

🔹 What is @Host() in DI?
Restricts dependency resolution to the component’s host element tree.

🔹 How to create a service per component instance?
Provide it in the providers array of the component.

🔹 What is InjectionToken used for?
To define a custom token for non-class based dependencies (like config objects).

🧨 RXJS HIGH-LEVEL OPERATORS

🔹 What is exhaustMap() good for?
Ignores new emissions while a previous observable is still active – perfect for login flows.

🔹 What does shareReplay() do?
Caches and multicasts the last emitted value – avoids duplicate HTTP calls.

🔹 When to use concatMap()?
When you want to queue Observables and maintain the order of execution.

🔹 Difference: mergeMap vs switchMap?
mergeMap = parallel, switchMap = cancels previous, picks latest.

🏗️ STRUCTURE & ARCHITECTURE

🔹 What is a core module pattern?
Single-time loaded module for app-wide services and configurations.

🔹 What is singleton service scope in Angular?
A service provided in root (via @Injectable) is a singleton across the app.

🔹 What is barrel file and why use it?
Index.ts that re-exports from a folder – simplifies import paths.

🔹 What is NX Monorepo in Angular?
Workspace for managing multiple Angular apps/libraries with shared tooling.

🚀 NEXT-GEN CONCEPTS (Angular 17+ & 18)

🔹 What are deferred views?
A way to lazy-load and hydrate views only when needed using *ngIf.defer.

🔹 What is control flow syntax in Angular 17?
New @if, @for, @switch replaces verbose structural directives.

🔹 What is signal-based input?
Use input({ signal: true }) to receive reactive input changes using Signals.

🔹 What is Zoneless Angular?
Upcoming approach to remove zone.js dependency, relies on Signals and reactive primitives.

🔄 LIFECYCLE EDGE CASES

🔹 Can ngOnChanges fire before ngOnInit?
Yes, it runs on any change to @Input() even before init.

🔹 When does ngOnDestroy NOT fire?
If the app crashes unexpectedly or Angular doesn’t unmount properly.

🔹 Can a service have lifecycle hooks?
No, only components/directives can.

🌍 INTERNATIONALIZATION (i18n)

🔹 What is Angular’s i18n strategy?
Compile-time translation using i18n attributes and ng extract-i18n.

🔹 What is the use of $localize?
Tagged template literal for runtime internationalization.

🔹 How to support multiple languages?
Use Angular i18n + message files (.xlf, .json) + build per locale.

🧠 TYPING + TS POWER IN ANGULAR

🔹 What is ReadonlyArray<T> vs T[]?
Immutable array – prevents mutation operations like .push().

🔹 Why use Partial<T> in input forms?
To allow partial object creation (e.g., for patching forms).

🔹 What is Record<string, any> used for?
Generic type-safe object with arbitrary keys – ideal for config or dictionary maps.

Next-Level One-Liner QnAs on Angular + JS + HTML + CSS?

No filler, just pure gold for Sr. Frontend Interviews, FAANG grind, and Architect vibes.
Let’s drop the Volume 4: Full Stack Frontend Edition 💣.

⚡️ ANGULAR – Expert One-Liner QnAs

🔹 How to memoize expensive pipes?
Use pure: true + OnPush + custom logic or memoizeOne() in pure functions.

🔹 How to persist app state between reloads?
Use localStorage + sync with BehaviorSubject in a service.

🔹 How does ViewEngine differ from Ivy?
ViewEngine = old renderer; Ivy = smaller bundles, better tree shaking, dynamic injection.

🔹 What’s Injector.create() used for?
Manual DI instance creation outside Angular context (useful in dynamic components).

🔹 How to trigger lazy route preload manually?
Use Router.preload() or set preloadingStrategy: PreloadAllModules.

🔹 How to listen to route param changes dynamically?
this.route.paramMap.subscribe() for real-time param updates.

🔹 How to pass data between unrelated components?
Use shared service with Subjects/Signals or Router state.

🔹 What is Zone-less Angular?
Upcoming mode replacing zone.js with Signals & effects to track change detection manually.

🧠 JavaScript – Brainy One-Liner QnAs

🔹 Difference: Object.freeze() vs Object.seal()?
freeze() = no change; seal() = can't add/remove props but can modify.

🔹 What is a closure?
Function + lexical environment bundle = memory of outer scope even after execution.

🔹 What’s event loop in JS?
Orchestrator that handles sync/async tasks via call stack + task queues.

🔹 What is a Proxy in JS?
An object that wraps another object and traps (intercepts) operations like get/set.

🔹 What is Debounce vs Throttle?
Debounce = wait till pause; Throttle = limit rate (1 call per N ms).

🔹 What does Object.defineProperty() do?
Defines precise behavior of property (writable, enumerable, configurable).

🔹 How to deeply clone an object (without lodash)?
structuredClone(obj) in modern JS or JSON trick with limitations.

🔹 What’s Symbol used for?
Unique, immutable identifier – perfect for hiding object keys or enums.

🎨 CSS – Smart, Stylish One-Liner QnAs

🔹 What is specificity in CSS?
Weight of selector — inline > ID > class > tag.

🔹 What is stacking context?
Z-index boundaries formed by positioned elements; affects which elements overlay.

🔹 Difference: visibility: hidden vs display: none?
Hidden = invisible but takes space; None = removed from flow.

🔹 What does contain: layout do?
Limits reflow/paint scope to that element – huge performance boost.

🔹 Why use will-change property?
Hints browser for upcoming animation/transition = GPU boost.

🔹 How to create aspect-ratio responsive elements?
Use aspect-ratio: 16 / 9; or padding-top trick (padding-top: 56.25%).

🔹 What’s isolation: isolate used for?
Starts new stacking context to fix z-index bleeding issues.

🔹 What is logical property in CSS?
Writing-mode-aware properties like margin-inline-start for LTR/RTL.

🧱 HTML – Pro-Level One-Liner QnAs

🔹 What does defer attribute on <script> do?
Delays script execution until HTML is parsed (but before DOMContentLoaded).

🔹 Difference: <section> vs <article> vs <div>?
Semantic containers: section = grouped topic, article = self-contained unit, div = generic.

🔹 What’s ARIA role and why is it important?
Defines accessibility semantics for screen readers (e.g., role="dialog").

🔹 Why prefer label[for] over nesting input inside label?
Better accessibility + easier styling/control separation.

🔹 How to lazy-load images in HTML?
Use <img loading="lazy" src="..."> – native and fast.

🔹 What is srcset and why use it?
Responsive images for different screen densities/devices.

🔹 How to prevent autofill in forms?
Use autocomplete="off" + fake hidden fields (browsers ignore simple autocomplete off).

🔗 Cross-Topic 🔥 Pro Scenarios

🔹 How to optimize Angular app for Core Web Vitals?
Lazy load modules, compress images, use ngOptimizedImage, enable SSR, defer scripts.

🔹 How to build SEO-friendly Angular SPA?
SSR (Angular Universal), dynamic <title>, meta, pre-rendering via ng express.

🔹 How to detect memory leaks in Angular?
Use Chrome DevTools + takeUntil + ngOnDestroy or ngProfiler.

🔹 Best way to implement reusable modal in Angular?
Dynamic component + service + overlay container with Injector.

🔹 How to integrate AI/Chatbot in Angular?
Use OpenAI API + reactive form + chat UI + streaming via ReadableStream.