Section 1: Angular Basics (1–15)
1. What is Angular?
Answer:
Angular is a TypeScript-based, open-source front-end framework developed by Google for building Single Page Applications (SPAs). It follows a component-based architecture and provides features like dependency injection, routing, forms, HTTP communication, and RxJS for reactive programming.
2. What are the features of Angular?
Answer:
Component-based architecture
Dependency Injection (DI)
Two-way Data Binding
Routing
Lazy Loading
Reactive Forms
RxJS Observables
Directives
Pipes
Built-in Testing Support
TypeScript support
Ahead-of-Time (AOT) Compilation
3. What is SPA?
Answer:
SPA (Single Page Application) loads a single HTML page and dynamically updates content without reloading the entire page.
Examples:
Advantages:
Fast navigation
Better user experience
Reduced server load
4. Difference between AngularJS and Angular?
| AngularJS | Angular |
|---|
| JavaScript | TypeScript |
| MVC | Component-based |
| Controllers | Components |
| Poor Performance | Better Performance |
| No Mobile Support | Mobile Friendly |
| No Lazy Loading | Supports Lazy Loading |
5. Why Angular uses TypeScript?
Answer:
TypeScript provides:
6. What is a Component?
Answer:
A Component controls a specific portion of the UI.
Example:
EmployeeComponent
employee.component.ts
employee.component.html
employee.component.css
7. What is Module?
Answer:
A Module groups related components, directives, services, and pipes.
Example:
AppModule
8. What is AppModule?
Answer:
AppModule is the root module where Angular application starts.
9. What is CLI?
Answer:
Angular CLI is a command-line tool used to create and manage Angular applications.
Examples:
ng new ProjectName
ng serve
ng build
ng test
10. Difference between Component and Module?
| Component | Module |
|---|
| Controls UI | Groups Components |
| HTML + TS + CSS | Collection |
| Reusable | Root Configuration |
11. What is Metadata?
Answer:
Metadata tells Angular how to process a class.
Example:
@Component({
selector:'app-home',
templateUrl:'home.component.html'
})
12. What is Decorator?
Answer:
Decorators are special functions that add metadata.
Examples:
@Component
@NgModule
@Injectable
@Input
@Output
13. What is Bootstrapping?
Answer:
Bootstrapping is the process of loading the root Angular component during application startup.
14. What is main.ts?
Answer:
It is the application's entry point.
Flow:
main.ts
↓
AppModule
↓
AppComponent
15. Explain Angular Architecture.
Browser
↓
main.ts
↓
AppModule
↓
Components
↓
Services
↓
HttpClient
↓
.NET API
↓
Database
Section 2: Data Binding (16–22)
16. What is Data Binding?
Answer:
Data Binding synchronizes data between the component and the HTML template.
17. Types of Data Binding?
Interpolation
Property Binding
Event Binding
Two-way Binding
18. What is Interpolation?
{{employeeName}}
Displays component data in HTML.
19. Property Binding?
<img [src]="image">
20. Event Binding?
<button (click)="Save()">
21. Two-way Binding?
[(ngModel)]
Example:
<input [(ngModel)]="employee.name">
22. Difference between Property and Event Binding?
| Property | Event |
|---|
| Component → View | View → Component |
Section 3: Directives (23–30)
23. What is Directive?
A Directive changes the appearance or behavior of DOM elements.
24. Types of Directives?
Component
Structural
Attribute
25. What is *ngIf?
Shows or hides an element.
<div *ngIf="isAdmin">
26. What is *ngFor?
Displays a list.
<li *ngFor="let emp of employees">
27. What is ngSwitch?
Displays content based on conditions.
28. What is ngClass?
Adds dynamic CSS classes.
29. What is ngStyle?
Applies dynamic styles.
30. Difference between ngIf and hidden?
| ngIf | hidden |
|---|
| Removes DOM | Hides Element |
Section 4: Components (31–40)
31. Lifecycle Hooks?
constructor
ngOnChanges
ngOnInit
ngDoCheck
ngAfterContentInit
ngAfterViewInit
ngOnDestroy
32. Difference between constructor and ngOnInit?
| Constructor | ngOnInit |
|---|
| Dependency Injection | Initialization |
| Runs first | Runs after constructor |
33. What is ngOnDestroy?
Used to clean up resources and unsubscribe from Observables to prevent memory leaks.
34. Parent to Child Communication?
@Input()
35. Child to Parent Communication?
@Output()
EventEmitter
36. ViewChild?
Access child component or DOM elements.
37. ContentChild?
Access projected content using <ng-content>.
38. Change Detection?
Angular checks the component tree for data changes and updates the view.
39. OnPush Change Detection?
Improves performance by checking changes only when inputs or Observable references change.
40. Standalone Components?
Angular 14+ allows components without NgModule.
Section 5: Services & Dependency Injection (41–50)
41. What is Service?
A Service contains reusable business logic and API communication.
42. Why use Services?
Code reuse
Separation of concerns
API calls
Shared state
43. What is Dependency Injection?
DI automatically provides instances of services to components.
44. What is @Injectable?
Marks a class as available for DI.
45. Singleton Service?
A service provided at the root level; only one instance exists across the application.
46. How to inject a Service?
constructor(private employeeService: EmployeeService) {}
47. What is provider?
Registers a service with Angular's injector.
48. Service Scope?
49. Difference between Component and Service?
| Component | Service |
|---|
| UI Logic | Business Logic |
50. Why shouldn't API calls be in Components?
To keep components lightweight, reusable, and easier to test.
Section 6: HTTP & RxJS (51–65)
51. How do you call a .NET Web API?
Using Angular HttpClient.
this.http.get<Employee[]>('/api/employees');
52. What is HttpClient?
A built-in Angular service used to make HTTP requests.
53. Difference between GET and POST?
GET retrieves data.
POST creates new data.
54. Difference between PUT and PATCH?
55. What is an Observable?
An asynchronous data stream provided by RxJS.
56. Difference between Observable and Promise?
| Observable | Promise |
|---|
| Multiple values | Single value |
| Cancelable | Not cancelable |
| Lazy | Eager |
57. What is subscribe()?
Used to receive data emitted by an Observable.
58. What is pipe()?
Allows chaining RxJS operators.
59. Common RxJS operators?
map
filter
tap
switchMap
mergeMap
concatMap
debounceTime
distinctUntilChanged
catchError
retry
finalize
60. What is Subject?
Acts as both an Observable and an Observer, allowing multicasting.
61. What is BehaviorSubject?
A Subject that stores the latest value and immediately emits it to new subscribers.
62. When would you use BehaviorSubject?
For sharing application state such as logged-in user or theme.
63. What is switchMap?
Switches to a new Observable and cancels the previous one—useful for search boxes.
64. What is debounceTime()?
Delays emissions to reduce frequent API calls during typing.
65. How do you handle HTTP errors?
Use catchError() in the service or an HTTP interceptor for centralized handling.
Section 7: Routing (66–75)
66. What is Routing in Angular?
Answer
Routing enables navigation between different components in a Single Page Application (SPA) without reloading the browser.
For example:
Dashboard
↓
Employees
↓
Employee Details
↓
Employee Edit
Angular uses the @angular/router package to manage routes.
Example:
const routes: Routes = [
{ path: '', component: HomeComponent },
{ path: 'employees', component: EmployeeComponent },
{ path: 'about', component: AboutComponent }
];
67. How do you configure Routes?
Answer
Routes are configured inside app-routing.module.ts.
const routes: Routes = [
{
path:'employees',
component:EmployeeComponent
},
{
path:'dashboard',
component:DashboardComponent
}
];
Import the routing module:
@NgModule({
imports:[RouterModule.forRoot(routes)],
exports:[RouterModule]
})
68. What is RouterOutlet?
Answer
<router-outlet> is a placeholder where Angular loads the routed component.
Example
<router-outlet></router-outlet>
Without router-outlet, Angular cannot display routed pages.
69. Difference between RouterLink and href?
| RouterLink | href |
|---|
| Angular navigation | Browser navigation |
| No page reload | Full page reload |
| Faster | Slower |
| Recommended | Avoid inside Angular |
Example
<a routerLink="/employees">Employees</a>
70. What is Lazy Loading?
Answer
Lazy Loading loads feature modules only when the user navigates to them instead of loading the entire application at startup.
Benefits:
Faster startup
Better performance
Smaller bundle size
Example
{
path:'admin',
loadChildren:() =>
import('./admin/admin.module')
.then(m=>m.AdminModule)
}
71. Advantages of Lazy Loading?
Answer
72. What are Route Parameters?
Answer
Route parameters pass dynamic values in the URL.
Example
employees/101
employees/102
Configuration
{
path:'employee/:id',
component:EmployeeDetailComponent
}
Access
this.route.snapshot.params['id'];
73. What is ActivatedRoute?
Answer
ActivatedRoute provides access to route information such as:
Route parameters
Query parameters
URL segments
Route data
Example
constructor(private route:ActivatedRoute){}
ngOnInit(){
let id=this.route.snapshot.paramMap.get('id');
}
74. What is Route Resolver?
Answer
A Resolver loads data before navigating to a component.
Flow
Navigation
↓
Resolver
↓
API
↓
Component Opens
Benefits
75. What are Route Guards?
Answer
Route Guards protect routes by deciding whether navigation is allowed.
Types:
CanActivate
CanDeactivate
Resolve
CanLoad
CanMatch
Example
canActivate():boolean{
return this.authService.isLoggedIn();
}
Real-world example
Only authenticated users can access the Dashboard.
Section 8: Forms (76–85)
76. What are Template-driven Forms?
Answer
Template-driven forms use Angular directives in the HTML template and rely on ngModel.
Example
<input [(ngModel)]="employee.name">
Best for:
Small forms
Simple validation
77. What are Reactive Forms?
Answer
Reactive Forms define form controls in the TypeScript class, offering better scalability and testability.
Example
this.employeeForm=this.fb.group({
name:['',Validators.required],
email:['']
});
Advantages
Better validation
Dynamic forms
Unit testing
Complex business rules
78. What is FormGroup?
Answer
A FormGroup groups multiple form controls into a single object.
Example
this.form=new FormGroup({
name:new FormControl(),
email:new FormControl()
});
79. What is FormControl?
Answer
A FormControl represents a single input element.
Example
new FormControl('')
80. What is FormBuilder?
Answer
FormBuilder simplifies creating Reactive Forms.
Instead of
new FormGroup()
Use
this.fb.group({
name:[''],
email:['']
});
81. What are Validators?
Answer
Validators validate user input.
Common validators:
required
email
minlength
maxlength
pattern
Example
Validators.required
82. What is a Custom Validator?
Answer
Custom validators validate business-specific rules.
Example
export function ageValidator(control:AbstractControl){
if(control.value<18)
return {invalidAge:true};
return null;
}
83. What is FormArray?
Answer
FormArray manages a dynamic collection of controls.
Example
Employee
Phone 1
Phone 2
Phone 3
Useful when the number of controls changes dynamically.
84. What are Dynamic Forms?
Answer
Dynamic Forms allow form fields to be generated at runtime based on configuration or API data.
Example
Registration forms where questions change based on user role.
85. How do you Disable or Enable Controls?
Example
this.form.controls['name'].disable();
this.form.controls['name'].enable();
Section 9: Security (86–92)
86. Explain JWT Authentication.
Answer
JWT (JSON Web Token) authenticates users securely.
Flow
Login
↓
.NET API
↓
JWT Token
↓
Angular Stores Token
↓
Interceptor
↓
Authorization Header
↓
API validates JWT
Header
Authorization: Bearer Token
87. What are Route Guards?
Route Guards prevent unauthorized access.
Example
User Logged In?
↓
Yes
↓
Dashboard
↓
No
↓
Login
88. What is an HTTP Interceptor?
Answer
An Interceptor modifies HTTP requests and responses globally.
Uses
Attach JWT
Logging
Error handling
Request modification
Example
request.clone({
setHeaders:{
Authorization:'Bearer '+token
}
});
89. What is XSS?
Answer
Cross-Site Scripting (XSS) is an attack where malicious scripts are injected into web pages.
Angular prevents XSS by automatically sanitizing template bindings.
Avoid using innerHTML with untrusted input.
90. What is DomSanitizer?
Answer
DomSanitizer safely displays trusted HTML, URLs, or resources.
Example
this.sanitizer.bypassSecurityTrustHtml(html);
Use it cautiously and only with trusted content.
91. What is CORS?
Answer
CORS (Cross-Origin Resource Sharing) allows a frontend hosted on one domain to access APIs on another domain.
Example
Angular
localhost:4200
.NET API
localhost:5001
Enable CORS in ASP.NET Core.
92. What is CSRF?
Answer
CSRF (Cross-Site Request Forgery) tricks a user's browser into sending unwanted authenticated requests.
Protection methods:
Anti-forgery tokens
SameSite cookies
Token validation
When using JWT in Authorization headers (instead of cookies), CSRF risk is generally much lower.
Section 10: Performance (93–100)
93. How does Lazy Loading improve performance?
Only the required modules are downloaded, reducing the application's initial bundle size and improving startup time.
94. What is trackBy?
trackBy helps Angular identify list items uniquely when using *ngFor, preventing unnecessary DOM updates.
Example
trackById(index:number,item:any){
return item.id;
}
95. What is OnPush Change Detection?
OnPush reduces unnecessary change detection cycles by checking components only when:
This improves performance in large applications.
96. Difference between Pure and Impure Pipes?
| Pure Pipe | Impure Pipe |
|---|
| Executes only when input reference changes | Executes on every change detection cycle |
| Better performance | Slower |
| Default behavior | Use only when necessary |
97. What is Virtual Scrolling?
Virtual Scrolling renders only the visible items instead of the entire list.
Example:
This significantly improves rendering performance.
98. What is Tree Shaking?
Tree Shaking removes unused JavaScript code during the production build, reducing bundle size.
99. Difference between AOT and JIT?
| AOT | JIT |
|---|
| Compiles during build | Compiles in the browser |
| Faster startup | Slower startup |
| Smaller bundle | Larger bundle |
| Used in production | Used during development |
100. How do you optimize Angular applications?
Common techniques:
Lazy Loading
OnPush Change Detection
trackBy with *ngFor
Virtual Scrolling
Avoid unnecessary subscriptions
Unsubscribe in ngOnDestroy
Use the async pipe
Split feature modules
Optimize images and assets
Build with production configuration
Advanced Questions (101–115)
101. What are Angular Signals?
Signals, introduced in Angular 16, are a reactive state management primitive that automatically notifies Angular when state changes.
Example:
count = signal(0);
count.set(1);
count.update(v => v + 1);
Advantages:
102. Signals vs Observables?
| Signals | Observables |
|---|
| State management | Asynchronous streams |
| Synchronous reads | Async data/events |
| Simpler syntax | Rich RxJS operators |
| Great for UI state | Great for HTTP, WebSockets, events |
103. What is NgRx?
NgRx is a Redux-inspired state management library for Angular.
Core concepts:
Store
Actions
Reducers
Effects
Selectors
Best suited for large enterprise applications with complex shared state.
104. What is State Management?
State Management is the process of storing and sharing application data consistently.
Options include:
105. What is Zone.js?
Zone.js patches asynchronous browser APIs (such as setTimeout, Promises, and DOM events) so Angular knows when asynchronous work completes and can trigger change detection automatically.
106. How does Angular Change Detection work?
Angular traverses the component tree and checks whether bound data has changed.
Strategies:
For better performance, use immutable data with OnPush.
107. Explain Dependency Injection hierarchy.
Angular resolves dependencies through a hierarchy of injectors.
Common scopes:
Angular searches from the nearest injector upward until it finds the requested service.
108. What are Standalone APIs?
Standalone APIs allow Angular applications to work without NgModule.
Example:
@Component({
standalone: true,
imports: [CommonModule]
})
export class EmployeeComponent {}
Benefits:
109. What is Angular Universal?
Angular Universal enables Server-Side Rendering (SSR).
Benefits:
110. How do you optimize Angular performance in enterprise applications?
Lazy-load feature modules
Use OnPush
Implement trackBy
Use virtual scrolling
Cache API responses
Minimize unnecessary subscriptions
Use production builds (AOT)
Optimize images and assets
Split large components
Use Signals or efficient state management
111. What is a Microfrontend architecture?
Microfrontends split a large frontend into independently developed and deployed applications.
Benefits:
112. How do you implement Role-Based Authorization?
User logs in.
Backend returns a JWT containing roles/claims.
Angular stores the token.
Route Guards verify roles before navigation.
Backend also validates the role for every protected API.
Never rely only on frontend checks; always enforce authorization on the server.
113. How do you securely store JWT tokens?
Recommended practices:
Prefer secure, HttpOnly cookies for high-security applications when architecture permits.
If using browser storage, understand the XSS risks and keep token lifetimes short.
Always use HTTPS.
Implement refresh tokens and token expiration.
Never hardcode secrets in the Angular application.
114. How do you integrate Angular with an ASP.NET Core Web API?
Flow:
Angular Component
↓
Angular Service (HttpClient)
↓
ASP.NET Core Web API
↓
Business Layer
↓
Entity Framework Core
↓
SQL Server
Use JWT authentication, centralized HTTP interceptors, proper error handling, and RESTful APIs.
115. Explain an end-to-end Login Flow using Angular, JWT, and ASP.NET Core.
Step 1: User enters credentials in Angular.
Step 2: Angular sends a POST request to the ASP.NET Core login API.
Step 3: The backend validates the credentials and generates a JWT containing user claims.
Step 4: Angular stores the token securely (based on your application's security approach).
Step 5: An HTTP Interceptor automatically adds the Authorization: Bearer <token> header to subsequent API requests.
Step 6: ASP.NET Core middleware validates the JWT before executing protected endpoints.
Step 7: Route Guards prevent unauthorized users from accessing protected pages.
Step 8: On token expiration, the application either redirects the user to log in again or uses a refresh-token mechanism if implemented.
