💡 Top 100+ Angular Interview Questions and Answers (Basic to Advanced) with Examples

 🧠 Introduction

Angular is one of the most powerful front-end frameworks for building dynamic single-page applications (SPAs).
This article will help you prepare for Angular interviews — whether you’re a beginner or senior developer — with clear explanations, code examples, and version comparisons (from AngularJS to Angular 17).

---

🟢 Section 1: Basic Angular Interview Questions

1. What is Angular?

Answer:
Angular is a TypeScript-based front-end framework developed by Google for building dynamic, responsive web applications.

It provides features like:

• Two-way data binding

• Dependency Injection (DI)

• Directives, Components, Services

• Routing and Forms handling

Example:

@Component({
  selector: 'app-hello',
  template: `<h1>Hello Angular!</h1>`
})
export class HelloComponent {}

---

2. What are Components in Angular?

Answer:
Components are the building blocks of an Angular app.
They control a part of the UI through a template, logic (TypeScript), and styles (CSS).

Structure:

@Component({
  selector: 'app-user',
  templateUrl: './user.component.html',
  styleUrls: ['./user.component.css']
})
export class UserComponent {
  name = 'Hasitha';
}

---

3. What is a Module in Angular?

Answer:
A module (@NgModule) is a container for components, directives, pipes, and services.

Example:

@NgModule({
  declarations: [AppComponent, UserComponent],
  imports: [BrowserModule],
  bootstrap: [AppComponent]
})
export class AppModule {}

---

4. What are Directives?

Answer:
Directives are instructions in the DOM.

• Structural Directives: *ngIf, *ngFor

• Attribute Directives: ngStyle, ngClass

Example:

<p *ngIf="isVisible">This is visible!</p>
<li *ngFor="let item of list">{{ item }}</li>

---

5. What is Data Binding?

Answer:
It connects the component logic and template view.

Type	Syntax	Example
Interpolation	{{}}	{{name}}
Property Binding	[property]	<img [src]="imageUrl">
Event Binding	(event)	<button (click)="onClick()">
Two-way Binding	[(ngModel)]	<input [(ngModel)]="username">

---

🧩 Section 2: Intermediate Angular Interview Questions

6. What is Dependency Injection (DI)?

Answer:
A design pattern in which a class receives its dependencies from an external source rather than creating them itself.

Example:

@Injectable()
export class UserService {
  getUsers() { return ['Hasitha', 'Cherry']; }
}

@Component({ ... })
export class UserComponent {
  constructor(private userService: UserService) {}
}

---

7. What are Pipes in Angular?

Answer:
Pipes transform data in the template.

Example:

<p>{{ today | date:'fullDate' }}</p>
<p>{{ 1234.56 | currency:'INR' }}</p>

Custom Pipe:

@Pipe({ name: 'capitalize' })
export class CapitalizePipe implements PipeTransform {
  transform(value: string): string {
    return value.toUpperCase();
  }
}

---

8. What is Routing in Angular?

Answer:
Routing allows navigation between different views (components).

Example:

const routes: Routes = [
  { path: 'home', component: HomeComponent },
  { path: 'about', component: AboutComponent }
];
@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule]
})
export class AppRoutingModule {}

---

9. What are Observables in Angular?

Answer:
Observables (from RxJS) are used to handle asynchronous data streams like HTTP requests or user input events.

Example:

this.http.get('https://api.example.com/users')
  .subscribe(data => console.log(data));

---

10. What are Lifecycle Hooks?

Answer:
Hooks allow developers to tap into component life events.

Hook	Description
ngOnInit()	Runs after component initialization
ngOnChanges()	Runs when input properties change
ngOnDestroy()	Runs before component destruction

Example:

ngOnInit() {
  console.log('Component initialized');
}

---

🔥 Section 3: Advanced Angular Interview Questions

11. What is Change Detection in Angular?

Answer:
Angular automatically checks and updates the DOM when data changes.
You can control this using ChangeDetectionStrategy.OnPush for performance.

@Component({
  selector: 'app-demo',
  template: `{{user.name}}`,
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class DemoComponent { }

---

12. What are Guards in Angular Routing?

Answer:
Guards control access to routes (like authentication).

Example:

@Injectable()
export class AuthGuard implements CanActivate {
  canActivate(): boolean {
    return !!localStorage.getItem('token');
  }
}

---

13. What is Lazy Loading?

Answer:
Lazy loading loads feature modules on demand to reduce initial load time.

Example:

const routes: Routes = [
  { path: 'admin', loadChildren: () => import('./admin/admin.module').then(m => m.AdminModule) }
];

---

14. What is Ahead-of-Time (AOT) Compilation?

Answer:
AOT compiles Angular templates at build time (not runtime), making apps faster.

---

15. What are Standalone Components (Angular 15+)?

Answer:
Angular 15 introduced standalone components that don’t require NgModule.

Example:

@Component({
  standalone: true,
  selector: 'app-hello',
  template: `<h1>Hello Standalone!</h1>`,
  imports: [CommonModule]
})
export class HelloComponent {}

---

🧱 Section 4: Important TypeScript Topics for Angular

TypeScript Feature	Description	Example
Interfaces	Defines structure of objects	interface User { name: string; age: number; }
Generics	Reusable type-safe code	function identity<T>(arg: T): T { return arg; }
Decorators	Add metadata to classes	@Component({...})
Enums	Define constants	enum Color { Red, Green, Blue }
Access Modifiers	Control visibility	private, public, protected
Async/Await	Simplify Promises	await this.http.get()

---

⚖️ Section 5: Major Differences Between Angular Versions

Feature	AngularJS (1.x)	Angular 2–8	Angular 9–13	Angular 14–17
Language	JavaScript	TypeScript	TypeScript	TypeScript
Architecture	MVC	Component-based	Ivy Compiler	Standalone Components
Mobile Support	No	Yes	Yes	Yes
Compilation	Runtime (JIT)	AOT supported	Ivy Renderer	Next-gen compiler
Forms	ng-model	Reactive & Template-driven	Improved forms API	Typed Forms
Routing	$routeProvider	RouterModule	Lazy Loading	Enhanced standalone routing
Build Tool	Grunt/Gulp	Angular CLI	Angular CLI	Vite integration (Angular 17)

---

🧰 Section 6: Common Angular Coding Questions

Example 1: Two-Way Data Binding

<input [(ngModel)]="userName">
<p>{{ userName }}</p>

Example 2: Using HTTPClient

this.http.get('https://api.example.com/posts')
  .subscribe(posts => this.posts = posts);

Example 3: Parent to Child Communication

// parent.component.html
<app-child [data]="userData"></app-child>

// child.component.ts
@Input() data: any;

Example 4: Custom Directive

@Directive({ selector: '[appHighlight]' })
export class HighlightDirective {
  constructor(el: ElementRef) {
    el.nativeElement.style.backgroundColor = 'yellow';
  }
}

---

🎯 Final Tips for Angular Interviews

✅ Revise core concepts: Components, Services, Observables, DI
✅ Write small sample projects using Angular CLI
✅ Understand TypeScript fundamentals
✅ Learn performance techniques (Lazy Loading, OnPush, AOT)
✅ Know version updates from Angular 2 → 17

Angular interview questions, Angular 17 questions, Angular advanced interview, Angular TypeScript topics, Angular code examples, Angular version comparison, Angular developer interview, Angular coding round

🚀 How to Improve Performance in C# — Code Refactoring and Optimization Guide

 🧠 Introduction

Performance plays a crucial role in any C# or .NET application. As your application grows, inefficient code and unnecessary computations can slow it down drastically.
To keep your app fast, scalable, and maintainable, you must regularly perform code refactoring and optimization.

In this article, you’ll learn:

• What performance optimization means in C#

• Refactoring techniques to simplify and speed up your code

• Real-time C# examples to apply in your project

• Best practices for memory management and efficiency

---

⚙️ What is Code Optimization?

Code Optimization is the process of making your C# code run faster and use fewer resources — without changing its output or functionality.

Example:

// Before Optimization
string result = "";
for (int i = 0; i < 10000; i++)
{
    result += i.ToString(); // Creates new string each time — inefficient
}

// After Optimization using StringBuilder
StringBuilder sb = new StringBuilder();
for (int i = 0; i < 10000; i++)
{
    sb.Append(i);
}
string result = sb.ToString(); // Much faster and memory efficient

👉 Why?
String is immutable in C#, meaning every concatenation creates a new object in memory. StringBuilder avoids this, improving speed and reducing garbage collection pressure.

---

🧩 What is Code Refactoring?

Refactoring means restructuring existing code to make it cleaner, readable, and maintainable — without changing its external behavior.

Example:

// Before Refactoring
if (user.Age >= 18)
{
    if (user.HasDrivingLicense)
    {
        Console.WriteLine("Eligible to drive");
    }
}

// After Refactoring (Better readability)
if (IsEligibleToDrive(user))
{
    Console.WriteLine("Eligible to drive");
}

bool IsEligibleToDrive(User user) => user.Age >= 18 && user.HasDrivingLicense;

✅ Benefits of Refactoring:

• Improves readability and maintainability

• Reduces duplicate code

• Makes debugging and testing easier

• Helps spot performance bottlenecks

---

⚡ Top Techniques to Improve Performance in C#

1. Use Appropriate Data Structures

Choose the right collection for your need:

// ❌ Wrong: List lookup O(n)
if (myList.Contains(id)) { ... }

// ✅ Right: HashSet lookup O(1)
if (myHashSet.Contains(id)) { ... }

Tip:
Use Dictionary<TKey, TValue> for key-value pairs, and HashSet<T> for quick lookups.

---

2. Avoid Unnecessary LINQ Queries

LINQ is powerful but can be slow for large datasets.

// ❌ Multiple enumerations
var activeUsers = users.Where(u => u.IsActive);
int count = activeUsers.Count();
var first = activeUsers.FirstOrDefault();

// ✅ Single enumeration
var activeUsersList = users.Where(u => u.IsActive).ToList();
int count = activeUsersList.Count;
var first = activeUsersList.FirstOrDefault();

---

3. Use Asynchronous Programming

Leverage async/await for I/O operations like file access, web API calls, or database queries.

// ❌ Blocking call
var data = GetData();
Console.WriteLine(data);

// ✅ Non-blocking
var data = await GetDataAsync();
Console.WriteLine(data);

Async improves responsiveness, especially in web and desktop applications.

---

4. Minimize Object Creation

Avoid creating objects repeatedly inside loops.

// ❌ Creates object each time
for (int i = 0; i < 1000; i++)
{
    var obj = new HeavyObject();
    obj.DoWork();
}

// ✅ Create once and reuse
var obj = new HeavyObject();
for (int i = 0; i < 1000; i++)
{
    obj.DoWork();
}

---

5. Use Caching Strategically

For expensive operations (like database or API calls), use caching.

private static readonly Dictionary<int, string> _cache = new();

public string GetUserName(int userId)
{
    if (_cache.ContainsKey(userId))
        return _cache[userId];

    string name = GetUserFromDatabase(userId);
    _cache[userId] = name;
    return name;
}

---

6. Avoid Boxing and Unboxing

When value types are treated as objects, C# performs boxing/unboxing, which is expensive.

// ❌ Causes boxing
ArrayList list = new ArrayList();
list.Add(10); // int -> object (boxed)

// ✅ Use Generics
List<int> list = new List<int>();
list.Add(10);

---

7. Dispose Unused Resources

Always use using statements for disposable objects like files, streams, or database connections.

using (SqlConnection con = new SqlConnection(connectionString))
{
    con.Open();
    // perform DB operations
} // Automatically disposes

---

8. Optimize Database Calls

• Use stored procedures instead of raw queries.

• Use Dapper or EF Core compiled queries for better performance.

• Avoid fetching unnecessary columns or rows.

Example:

// ❌ Bad
var users = db.Users.ToList(); // loads all users

// ✅ Good
var users = db.Users.Where(u => u.IsActive).Select(u => new { u.Id, u.Name }).ToList();

---

🧮 Memory Optimization Tips

• Use structs instead of classes for small, immutable types.

• Avoid large arrays or lists in memory — consider streaming or pagination.

• Use Span<T> or Memory<T> for performance-sensitive operations.

• Use pooling for frequently reused objects.

---

🧰 Tools for Performance and Refactoring

1. Visual Studio Diagnostic Tools – Analyze CPU and memory usage

2. dotTrace / dotMemory (JetBrains) – Find bottlenecks

3. ReSharper – Suggests code refactoring opportunities

4. BenchmarkDotNet – Compare method performance

5. SonarQube – Code quality and maintainability analysis

---

✅ Summary

Category	Tip	Benefit
Strings	Use StringBuilder	Reduces memory allocations
Collections	Choose right data structure	Faster lookups
Async	Use async/await	Improves responsiveness
Memory	Dispose resources	Avoid leaks
LINQ	Minimize queries	Faster execution
Caching	Cache frequent data	Saves database hits
Refactoring	Clean, modular code	Easier maintenance

---

✨ Final Thoughts

Performance optimization in C# isn’t about premature tweaking — it’s about writing clean, efficient, and maintainable code.
By combining refactoring principles with smart optimization techniques, you can build .NET applications that are both fast and future-proof.

🧱 Understanding the Core Building Blocks of Angular

 

🌟 Introduction

Angular is one of the most powerful front-end frameworks used for developing modern single-page applications (SPAs). What makes Angular unique is its structured architecture, which is built upon several key building blocks.

In this article, we’ll explore these core Angular building blocks—Modules, Components, Templates, Directives, Services, Pipes, and Routing—with clear explanations and examples to help you understand how they all work together.

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1. 🧩 Modules (NgModule)

Modules are the organizational units of an Angular application. They group related components, directives, pipes, and services together into a cohesive block of functionality.

Every Angular app has at least one root module called AppModule, defined in the app.module.ts file.

✅ Example:

@NgModule({
  declarations: [AppComponent, HomeComponent],
  imports: [BrowserModule, FormsModule],
  bootstrap: [AppComponent]
})
export class AppModule { }

💡 Purpose:

• Organizes code into functional areas.

• Supports lazy loading for better performance.

• Simplifies dependency management.

---

2. ⚙️ Components

Components are the heart of Angular applications. Each component controls a specific section of the UI and defines its behavior and appearance.

A component is made up of:

• HTML Template (View)

• TypeScript Class (Logic)

• CSS/SCSS Styles (Design)

✅ Example:

@Component({
  selector: 'app-hello',
  template: `<h1>Hello {{name}}!</h1>`,
  styles: [`h1 { color: blue; }`]
})
export class HelloComponent {
  name = 'Angular';
}

💡 Purpose:

• Defines the UI logic and view.

• Reusable across the application.

• Connects data and behavior using data binding.

---

3. 🧾 Templates

Templates define what the user sees in the browser. They combine HTML with Angular directives, pipes, and binding expressions.

✅ Example:

<div *ngIf="isLoggedIn">
  Welcome, {{ userName | uppercase }}
</div>

💡 Purpose:

• Defines the layout and structure of the component.

• Uses data binding ({{ }}) and directives (*ngIf, *ngFor) to make the view dynamic.

---

4. 🧭 Directives

Directives are used to add behavior or modify DOM elements in the template.

🧱 Types of Directives:

1. Structural Directives – Change the structure of the DOM (*ngIf, *ngFor)

2. Attribute Directives – Change the appearance or behavior of elements ([ngClass], [ngStyle])

✅ Example:

<p *ngIf="showMessage">Hello Angular!</p>
<button [disabled]="!isActive">Click Me</button>

💡 Purpose:

• Enhance HTML elements dynamically.

• Add custom interactive behaviors.

---

5. 🧠 Services & Dependency Injection

Services are used to share data or logic across multiple components. They are the backbone of business logic in Angular.

They often handle tasks like API calls, data fetching, and application-wide state management.

✅ Example:

@Injectable({ providedIn: 'root' })
export class DataService {
  getData() {
    return ['Apple', 'Banana', 'Cherry'];
  }
}

💡 Purpose:

• Promote code reusability.

• Keep components lightweight.

• Implement Dependency Injection (DI) for efficiency.

---

6. 🌐 Routing

Routing enables navigation between different views or pages without reloading the entire application. It’s what makes Angular apps behave like single-page applications.

✅ Example:

const routes: Routes = [
  { path: 'home', component: HomeComponent },
  { path: 'about', component: AboutComponent }
];

💡 Purpose:

• Manages navigation within the app.

• Supports lazy loading and guarding routes for security.

---

7. 🔄 Pipes

Pipes are used to transform data before displaying it in the template. Angular provides several built-in pipes such as uppercase, date, and currency. You can also create custom pipes.

✅ Example:

<p>{{ today | date:'fullDate' }}</p>

💡 Purpose:

• Simplify data formatting in templates.

• Reusable and easy to integrate.

---

📋 Summary Table

Building Block	Description	Example
Module	Organizes the application into logical units	AppModule
Component	Defines UI and logic	HomeComponent
Template	Defines the view’s HTML	<h1>{{title}}</h1>
Directive	Adds behavior to elements	*ngFor, *ngIf
Service	Shares data or logic	DataService
Routing	Manages navigation	/home, /about
Pipe	Formats or transforms data	`{{name

---

🎯 Conclusion

Angular’s building blocks work together to create a powerful, maintainable, and scalable application structure.
By mastering Modules, Components, Templates, Directives, Services, Pipes, and Routing, developers can build high-performing web applications with ease and flexibility.

Whether you’re a beginner or an experienced developer, understanding these building blocks is the first step toward becoming an Angular expert. 

🧠 What is Generics in C#? Complete Guide with Examples

 📘 Introduction

In C#, Generics are one of the most powerful features introduced with the .NET Framework 2.0.
They allow you to define classes, methods, interfaces, and collections that can work with any data type — while still maintaining type safety and performance.

In simple words, Generics help you write code once and use it with any data type.

---

⚙️ What Are Generics?

Generics let you define a placeholder type (called a type parameter) that will be replaced with a specific type when you create an instance of a class or call a method.

This means you can write:

List<int>
List<string>
List<Employee>

—all using the same generic List<T> class.

---

💡 Example Without Generics

public class Calculator
{
    public int Add(int a, int b)
    {
        return a + b;
    }
}

If you want to add float or double values, you’ll have to write multiple methods for each data type.
This leads to code duplication and poor reusability.

---

⚙️ Example With Generics

public class Calculator<T>
{
    public T Add(T a, T b)
    {
        dynamic x = a;
        dynamic y = b;
        return x + y;
    }
}

class Program
{
    static void Main()
    {
        Calculator<int> intCalc = new Calculator<int>();
        Console.WriteLine("Sum (int): " + intCalc.Add(10, 20));

        Calculator<double> doubleCalc = new Calculator<double>();
        Console.WriteLine("Sum (double): " + doubleCalc.Add(10.5, 20.7));
    }
}

✅ Output

Sum (int): 30
Sum (double): 31.2

Here, T is a type parameter. It allows the Calculator class to operate with any data type (int, double, string, etc.).

---

🧱 Generic Method Example

You can also create generic methods inside normal classes.

public class DisplayData
{
    public void ShowData<T>(T data)
    {
        Console.WriteLine("Value: " + data);
    }
}

class Program
{
    static void Main()
    {
        DisplayData obj = new DisplayData();
        obj.ShowData<int>(101);
        obj.ShowData<string>("Hello Generics");
    }
}

✅ Output

Value: 101
Value: Hello Generics

Here, the method ShowData<T>() can accept any data type without overloading.

---

📚 Generic Collections in C#

C# provides several built-in generic collections inside the System.Collections.Generic namespace.
These are type-safe and more efficient than old non-generic collections like ArrayList or Hashtable.

Generic Collection	Description
List<T>	Dynamic array of type T
Dictionary<TKey, TValue>	Key-value pair collection
Queue<T>	FIFO (First-In-First-Out) collection
Stack<T>	LIFO (Last-In-First-Out) collection

Example:

List<string> names = new List<string>();
names.Add("Hasitha");
names.Add("Cherry");

foreach (var name in names)
{
    Console.WriteLine(name);
}

✅ Output

Hasitha
Cherry

---

🧩 Benefits of Generics in C#

Benefit	Description
Type Safety	Prevents type mismatches at compile time
Performance	Avoids boxing/unboxing for value types
Reusability	Write code once, use with any type
Maintainability	Cleaner and less repetitive code

---

🔄 Generic Constraints (Optional but Powerful)

Sometimes, you might want to restrict which data types can be used with your generic class.

Example:

public class DataManager<T> where T : class
{
    public void Display(T data)
    {
        Console.WriteLine("Data: " + data);
    }
}

Here, where T : class means only reference types can be used.

---

🚀 Conclusion

Generics in C# make your code reusable, efficient, and type-safe.
They help developers build scalable and maintainable applications, especially in large projects using .NET Core or ASP.NET.