67 Angular interview questions with answers

All Angular interview questions

• What is Angular? How is it different from AngularJS, React and Vue?

• What parts make up an Angular component?

• What is a standalone component and why does Angular recommend it?

• How does modern Angular application bootstrapping work?

• What role do NgModules still play in modern Angular?

• What is the Angular lifecycle hook order and when should each hook be used?

• How do the Angular compiler and template type checking help production apps?

• How do interpolation, property binding and event binding differ?

• How does two-way binding with `[(ngModel)]` work?

• What are component inputs and outputs used for in Angular?

• How is signal input `input()` different from traditional `@Input()`?

• When should you use model input `model()`?

• What is a directive in Angular? How do structural directives differ from attribute directives?

• How do new control flow blocks `@if`, `@for`, `@switch` differ from `*ngIf`, `*ngFor`?

• Why is `track` important in `@for`?

• What is the `@defer` block used for?

• When should you use content projection with `ng-content`?

• What is a signal in Angular?

• How do `signal`, `computed` and `effect` differ?

• How are view queries different from content queries?

• In Angular, how do you bring async (HTTP) data into signal-based code? How does `toSignal()` differ from `resource()`?

• How do Observables and Signals differ in Angular?

• How does OnPush change detection work?

• What is zoneless Angular and when should you consider it?

• How does the `async` pipe help when using Observables in templates?

• How are pure pipes different from impure pipes?

• What is Dependency Injection in Angular?

• How is `providedIn: "root"` different from a component provider?

• How is `inject()` different from constructor injection?

• When should you use `InjectionToken`?

• How do hierarchical injectors affect state and memory leaks?

• How do provider strategies `useClass`, `useValue`, `useFactory`, and `useExisting` differ?

• What are the basics of Angular Router?

• How do you lazy load routes in modern Angular?

• Do route guards truly secure APIs?

• When should you use a resolver in Angular Router?

• How does `withComponentInputBinding()` help with route params?

• How do you read route params and query params in Angular?

• What problem do typed Reactive Forms solve?

• How do you write a custom validator in Reactive Forms?

• When should you use ControlValueAccessor?

• When should you use FormArray?

• How do Reactive Forms and Template-driven Forms differ in Angular? When do you use each?

• What is HttpClient used for in Angular?

• When should you use an HTTP interceptor?

• How do `switchMap`, `mergeMap`, `concatMap`, and `exhaustMap` differ in Angular?

• How do you avoid memory leaks when subscribing to Observables?

• Where should HTTP errors be handled in Angular?

• What problems do Angular SSR and hydration solve?

• What is hydration in Angular SSR? How does non-destructive hydration work?

• What are common hydration mismatch issues in Angular?

• Where should you start when optimizing an Angular bundle?

• How does Angular support accessibility (a11y)? What does the CDK a11y module provide?

• How are `animate.enter` and `animate.leave` different from legacy Angular animations?

• What is Angular TestBed used for?

• Does modern Angular CLI testing use Karma or Vitest?

• How do you test HttpClient in Angular?

• When does an Angular app need NgRx, Signal Store or another state management library?

• What is a safe process for migrating a legacy Angular app to a newer version?

• Should initialization code go in the `constructor` or `ngOnInit`? Why?

• With a signal holding an array/object, why does `items().push(x)` not update the UI? How do `set` and `update` differ?

• What causes `ExpressionChangedAfterItHasBeenCheckedError` (NG0100) and how do you fix it?

• A component uses `OnPush` but the UI does not update when data changes — how do you diagnose and fix it?

• How do you use `takeUntilDestroyed` correctly, and why does it sometimes throw NG0203?

• Migrating an Angular app to zoneless: what breaks and what must be fixed?

• When should you **not** use `effect()`? What do you use instead?

• Design a refresh-token flow with an HTTP interceptor: how do you keep concurrent 401s from triggering multiple refresh calls?