Prepare for your Angular frontend interviews with this comprehensive collection of 100 Angular interview questions and answers. Master essential concepts like components, services, directives, RxJS observables, routing, and state management. Whether you're preparing for frontend engineering roles or Angular developer positions, this guide covers everything from basic framework concepts to advanced Angular patterns. Boost your confidence with detailed explanations and practical examples for each question.Q1: What is Angular? basics
Angular Fundamentals
Angular is a TypeScript-based open-source framework for building dynamic web applications with a component-based architecture and powerful tooling.
Q2: What is a component? components
Angular Fundamentals
A component is a basic UI building block in Angular that encapsulates template, styles, and logic, marked with @Component decorator.
Q3: What is a service? services
Angular Fundamentals
A service is a reusable class marked with @Injectable that provides shared functionality, often used for API calls and data sharing.
Q4: What is dependency injection? core
Angular Fundamentals
Dependency injection is a design pattern where Angular automatically provides dependencies to components/services, improving testability and decoupling.
Q5: What is a module? modules
Angular Fundamentals
A module is a container for components, services, and other code organized with @NgModule decorator to group related features.
Q6: What is @NgModule? decorators
Angular Fundamentals
@NgModule is a decorator that defines a module, declaring components, services, imports, exports, and providers.
Q7: What is @Component? decorators
Angular Fundamentals
@Component is a decorator that marks a class as a component and defines its selector, template, and styles.
Q8: What is @Injectable? decorators
Angular Fundamentals
@Injectable is a decorator that marks a class as a service eligible for dependency injection.
Q9: What is a directive? directives
Angular Fundamentals
A directive is a marker on a DOM element that tells Angular to attach behavior or transform the DOM, like *ngIf or *ngFor.
Q10: What are structural directives? directives
Angular Fundamentals
Structural directives change DOM structure by adding/removing elements, e.g., *ngIf, *ngFor, *ngSwitch.
Q11: What are attribute directives? directives
Angular Fundamentals
Attribute directives change element appearance or behavior without affecting DOM structure, e.g., ngStyle, ngClass.
Q12: What is *ngIf? directives
Angular Fundamentals
*ngIf conditionally renders an element based on a boolean expression.
Q13: What is *ngFor? directives
Angular Fundamentals
*ngFor repeats template for each item in a list, e.g., *ngFor="let item of items".
Q14: What is *ngSwitch? directives
Angular Fundamentals
*ngSwitch conditionally renders different templates based on a switch value.
Q15: What is ngStyle? directives
Angular Fundamentals
ngStyle dynamically sets inline styles on an element based on an expression object.
Q16: What is ngClass? directives
Angular Fundamentals
ngClass dynamically applies CSS classes based on conditions or an object.
Q17: What is data binding? binding
Angular Fundamentals
Data binding synchronizes data between component class and template in one or two-way direction.
Q18: What is property binding? binding
Angular Fundamentals
Property binding sets a component/DOM property to a template expression using [property]="value" syntax.
Q19: What is event binding? binding
Angular Fundamentals
Event binding triggers a method when a DOM event occurs using (event)="handler()" syntax.
Q20: What is two-way binding? binding
Angular Fundamentals
Two-way binding syncs data bidirectionally using [(ngModel)]="property" syntax.
Q21: What is string interpolation? binding
Angular Fundamentals
String interpolation displays component data in template using {{expression}} syntax.
Q22: What is a template reference variable? templates
Angular Fundamentals
A template reference variable (#varName) provides direct access to a DOM element in the component class.
Q23: What is a pipe? pipes
Angular Fundamentals
A pipe transforms data in templates using the | syntax, e.g., {{ date | date:'short' }}.
Q24: What is the async pipe? pipes
Angular Fundamentals
The async pipe automatically subscribes to observables and displays their latest value in templates.
Q25: What is the date pipe? pipes
Angular Fundamentals
The date pipe formats dates according to locale rules, e.g., {{ date | date:'dd/MM/yyyy' }}.
Q26: What is the currency pipe? pipes
Angular Fundamentals
The currency pipe formats numbers as currency, e.g., {{ price | currency:'USD' }}.
Q27: What is the uppercase pipe? pipes
Angular Fundamentals
The uppercase pipe converts text to uppercase, e.g., {{ text | uppercase }}.
Q28: What is the lowercase pipe? pipes
Angular Fundamentals
The lowercase pipe converts text to lowercase, e.g., {{ text | lowercase }}.
Q29: What is RxJS? rxjs
Angular Fundamentals
RxJS is a library for reactive programming using observables, enabling handling of asynchronous operations.
Q30: What is an Observable? rxjs
Angular Fundamentals
An Observable is a lazy collection of events that can be observed over time using subscribe().
Q31: What is a Subject? rxjs
Angular Fundamentals
A Subject is a special observable that multicasts values to multiple subscribers.
Q32: What is a BehaviorSubject? rxjs
Angular Fundamentals
A BehaviorSubject is a subject that emits its current value to new subscribers immediately.
Q33: What is a ReplaySubject? rxjs
Angular Fundamentals
A ReplaySubject buffers and replays a specified number of values to new subscribers.
Q34: What is an AsyncSubject? rxjs
Angular Fundamentals
An AsyncSubject emits the last value of a sequence only when the observable completes.
Q35: What are operators? rxjs
Angular Fundamentals
Operators are functions that transform, filter, or combine observable values, e.g., map, filter, switchMap.
Q36: What is the map operator? rxjs
Angular Fundamentals
The map operator transforms observable values using a projection function.
Q37: What is the filter operator? rxjs
Angular Fundamentals
The filter operator emits only observable values that pass a predicate test.
Q38: What is the switchMap operator? rxjs
Angular Fundamentals
The switchMap operator projects each source value to an observable and flattens, canceling previous inner observables.
Q39: What is the mergeMap operator? rxjs
Angular Fundamentals
The mergeMap operator projects each value to an observable and flattens all inner observables.
Q40: What is the concat operator? rxjs
Angular Fundamentals
The concat operator sequentially concatenates multiple observables in order.
Q41: What is the merge operator? rxjs
Angular Fundamentals
The merge operator combines multiple observables and emits values from all simultaneously.
Q42: What is reactive forms? forms
Angular Fundamentals
Reactive forms provide a model-driven approach using FormGroup, FormControl for complex form handling.
Q43: What is template-driven forms? forms
Angular Fundamentals
Template-driven forms use directives in templates with ngModel for simpler form handling.
Q44: What is FormGroup? forms
Angular Fundamentals
FormGroup manages a group of FormControls, allowing validation and status tracking of the entire form.
Q45: What is FormControl? forms
Angular Fundamentals
FormControl is the lowest-level unit tracking value and validation status of an individual form field.
Q46: What is FormBuilder? forms
Angular Fundamentals
FormBuilder provides shortcuts for creating FormGroup and FormControl instances.
Q47: What are validators? forms
Angular Fundamentals
Validators are functions that check form control values and return errors if validation fails.
Q48: What is async validation? forms
Angular Fundamentals
Async validation validates form controls asynchronously, e.g., checking username availability from server.
Q49: What is the HttpClient? http
Angular Fundamentals
HttpClient is Angular's service for making HTTP requests to servers for communication.
Q50: What is an interceptor? http
Angular Fundamentals
An interceptor intercepts HTTP requests/responses to add headers, handle errors, or transform data.
Q51: What is the async pipe? pipes
Angular Fundamentals
The async pipe subscribes to observables and automatically unsubscribes when components destroy.
Q52: What is routing? routing
Angular Fundamentals
Routing enables navigation between different components/pages using URLs without full page reload.
Q53: What is RouterModule? routing
Angular Fundamentals
RouterModule provides routing functionality including Router, ActivatedRoute services and routes configuration.
Q54: What is the Router service? routing
Angular Fundamentals
The Router service navigates between components using navigate() or navigateByUrl() methods.
Q55: What is ActivatedRoute? routing
Angular Fundamentals
ActivatedRoute provides access to route parameters and query parameters of the current route.
Q56: What is a route guard? routing
Angular Fundamentals
A route guard (CanActivate, CanDeactivate, Resolve) controls access to routes based on conditions.
Q57: What is CanActivate? routing
Angular Fundamentals
CanActivate guard prevents access to a route based on conditions, e.g., authentication.
Q58: What is CanDeactivate? routing
Angular Fundamentals
CanDeactivate guard prevents navigation away from a route, e.g., unsaved form data warning.
Q59: What is Resolve? routing
Angular Fundamentals
Resolve guard pre-fetches data before activating a route, ensuring data is available when component loads.
Q60: What is lazy loading? routing
Angular Fundamentals
Lazy loading loads feature modules only when users navigate to them, improving initial load performance.
Q61: What is change detection? core
Angular Fundamentals
Change detection is Angular's mechanism to detect component state changes and update the view accordingly.
Q62: What is OnInit? lifecycle
Angular Fundamentals
OnInit is a lifecycle hook called once after component initialization, used for setup and initialization.
Q63: What is OnDestroy? lifecycle
Angular Fundamentals
OnDestroy is a lifecycle hook called before component destruction, used for cleanup and unsubscribing.
Q64: What is OnChanges? lifecycle
Angular Fundamentals
OnChanges is a lifecycle hook called when component receives input property changes.
Q65: What is DoCheck? lifecycle
Angular Fundamentals
DoCheck is a custom change detection hook called during every change detection cycle.
Q66: What is AfterViewInit? lifecycle
Angular Fundamentals
AfterViewInit is a lifecycle hook called after component view and child views initialize.
Q67: What is Input decorator? decorators
Angular Fundamentals
@Input allows parent components to pass data to child components via properties.
Q68: What is Output decorator? decorators
Angular Fundamentals
@Output allows child components to emit events to parent components using EventEmitter.
Q69: What is ViewChild? decorators
Angular Fundamentals
@ViewChild gets reference to a template element or child component in the component class.
Q70: What is ViewChildren? decorators
Angular Fundamentals
@ViewChildren gets references to multiple template elements or child components.
Q71: What is ContentChild? decorators
Angular Fundamentals
@ContentChild gets reference to projected content elements.
Q72: What is ContentChildren? decorators
Angular Fundamentals
@ContentChildren gets references to multiple projected content elements.
Q73: What is content projection? components
Angular Fundamentals
Content projection inserts component content into designated slots in child component template.
Q74: What is ng-content? templates
Angular Fundamentals
ng-content is a placeholder in component template where parent component content is inserted.
Q75: What is an element reference? templates
Angular Fundamentals
Element reference (template reference variable) provides direct access to DOM elements in component logic.
Q76: What is ElementRef? core
Angular Fundamentals
ElementRef wraps a native DOM element, providing access to the underlying native object.
Q77: What is Renderer2? core
Angular Fundamentals
Renderer2 is a service for safely manipulating DOM without direct native element access.
Q78: What are lifecycle hooks? lifecycle
Angular Fundamentals
Lifecycle hooks are callback methods called at specific moments during component lifecycle progression.
Q79: What is zone.js? core
Angular Fundamentals
Zone.js is a library providing execution context (zone) for change detection triggering in Angular.
Q80: What is NgZone? core
Angular Fundamentals
NgZone is Angular service for running code inside/outside Angular zone, controlling change detection.
Q81: What is property binding vs attribute binding? binding
Angular Fundamentals
Property binding sets DOM properties; attribute binding sets HTML attributes.
Q82: What is @HostBinding? decorators
Angular Fundamentals
@HostBinding binds a class property to host element's property or attribute.
Q83: What is @HostListener? decorators
Angular Fundamentals
@HostListener subscribes to host element events like click, mouseover, etc.
Q84: What is AOT compilation? build
Angular Fundamentals
AOT (Ahead-of-Time) compilation pre-compiles Angular application during build, improving performance.
Q85: What is JIT compilation? build
Angular Fundamentals
JIT (Just-in-Time) compilation compiles Angular application in the browser at runtime.
Q86: What is a module vs a component? core
Angular Fundamentals
A module organizes code; a component is an individual UI element with view and logic.
Q87: What is tree shaking? build
Angular Fundamentals
Tree shaking removes unused code during production build to reduce bundle size.
Q88: What is lazy loading modules? routing
Angular Fundamentals
Lazy loading loads feature modules only when needed, improving initial app load time.
Q89: What is providedIn? services
Angular Fundamentals
@Injectable({providedIn: 'root'}) provides service at root level, enabling tree-shaking.
Q90: What is testing in Angular? testing
Angular Fundamentals
Testing verifies Angular component behavior using Jasmine testing framework and Karma test runner.
Q91: What is Jasmine? testing
Angular Fundamentals
Jasmine is a JavaScript testing framework with describe, it, expect syntax for unit testing.
Q92: What is Karma? testing
Angular Fundamentals
Karma is a test runner that executes Jasmine tests in real browsers.
Q93: What is TestBed? testing
Angular Fundamentals
TestBed is an Angular testing utility for configuring modules and injecting services in tests.
Q94: What is fixture? testing
Angular Fundamentals
A fixture is a wrapper around a component, providing testing utilities for component interaction.
Q95: What is DebugElement? testing
Angular Fundamentals
DebugElement wraps component elements, providing testing utilities for querying and debugging.