Components are the building blocks of Angular applications . Every UI part—header, menu, product card, login screen, dashboard—is a component.
Understanding components deeply is the first and most important step in becoming a professional Angular developer. They define how your app looks, behaves, and interacts with users.
In this blog , you’ll learn everything about Angular components , their structure and lifecycle to advanced concepts like dynamic creation, content projection, and change detection.
What You’ll Learn
Understand the role of components in Angular architecture
Build reusable and dynamic components
Communicate effectively between components
Manage component lifecycle, styling, and optimization
Interview Questions
What are Components?
Components are the building blocks of an Angular app. Each component controls a specific section of the user interface, combining HTML (view), CSS (styling), and TypeScript (logic).
A component is a self-contained UI unit in Angular responsible for:
A component controls how a part of the UI looks and behaves.
Example Structure
user.component.ts
user.component.html
user.component.css
user.component.spec.ts
Why Components?
Angular follows a component-based architecture to:
Split UI into small, reusable pieces
Isolate logic for better maintainability
Improve code structure
Enable team collaboration (each dev works on separate components)
Improve readability & testing
Benefits
Reusable
Testable
Maintainable
Easy to debug
Scalable architecture
When Should You Create a Component?
Create a new component when
You need a reusable UI element
The UI part has its own logic and style
The screen is becoming too large
Multiple modules require the same feature
You want to organize your code
Examples
Header / Footer
Navbar
User card
Product list
Reusable form
Dialog / popup
How to Create a Component
Using CLI
ng generate component header
OR
ng g c header
This command creates a new component with below files .
header.component.ts
header.component.html
header.component.css
header.component.spec.ts
Component Syntax and Key Properties
Every component in Angular is defined by the @Component() decorator.
@Component({
selector: 'app-header',
templateUrl: './header.component.html',
styleUrls: ['./header.component.css'],
imports: []
})
export class HeaderComponent {
message = 'Hello Angular!';
}
Key Properties:
| Property | Purpose |
|---|
| selector | HTML tag used to call the component |
| templateUrl | View file |
| styleUrls | Component-level CSS |
| imports | Standalone components/modules |
Component Registration
Use inside app:
@Component({
selector: 'app-root',
imports: [HeaderComponent],
templateUrl: './app.html'
})
Add the component to the app.html template, for example:
<app-header></app-header>
Templates and Data Binding
Templates define the HTML structure of your component.
Angular provides data binding to connect the UI with component logic.
Four types of data binding:
Interpolation: {{ title }}
Property Binding: [src]="imageUrl"
Event Binding: (click)="onClick()"
Two-Way Binding: [(ngModel)]="userName"
Example
<h2>{{ title }}</h2>
<input [(ngModel)]="title" placeholder="Change title" />
<button (click)="reset()">Reset</button>
Component Communication
In real-world applications, components often need to communicate.
Parent → Child: @Input()
@Input() productName: string = '';
Child → Parent: @Output() and EventEmitter
@Output() notify = new EventEmitter<string>();
Sibling → Sibling: via Services
Using shared service with Subject/BehaviorSubject.
Lifecycle Hooks
Angular components go through a predictable series of events called lifecycle hooks.
Common ones include:
| Hook | Purpose |
|---|
| ngOnInit | Runs after component initialization |
| ngOnChanges | Runs when input property changes |
| ngOnDestroy | Runs when component is destroyed |
| ngAfterViewInit | Access DOM/Child components |
Example:
ngOnInit() {
console.log('Component initialized!');
}
ngOnDestroy() {
console.log('Component destroyed!');
}
Component Styling & View Encapsulation
Angular encapsulates component styles by default so they don’t leak into other parts of the app.
Encapsulation modes
Emulated (default): Angular scopes component styles using attribute selectors (simulated Shadow DOM).
None: Styles are applied globally without any encapsulation.
ShadowDom: Uses the browser’s native Shadow DOM to fully isolate component styles.
Example
@Component({
selector: 'app-banner',
templateUrl: './banner.component.html',
styleUrls: ['./banner.component.css'],
encapsulation: ViewEncapsulation.None
})
Dynamic Components
Sometimes, you need to create components on the fly — like modals, alerts, or tooltips.
Modern Approach (Angular 13+):
const componentRef = viewContainerRef.createComponent(MyDialogComponent);
Use ViewContainerRef to dynamically inject components into a placeholder.
Best Practices
Keep components small and focused
Use clear naming conventions (app-user-card, not card1)
Use shared modules for reusable components
Optimize with lazy loading
Follow accessibility standards
Interview Questions
1. What is an Angular component?
A component is a standalone, reusable UI unit containing template, logic, and styles.
2. What is the role of the @Component decorator?
It provides metadata for Angular to create and render the component.
3. Why are components important?
They make the application modular, reusable, and maintainable.
4. Difference: Standalone Component vs Module-based?
5. What is a selector?
The HTML tag used to render the component.
6. How to communicate between parent and child components?
7. What are lifecycle hooks in Angular?
Methods like ngOnInit, ngOnDestroy, used to control component behavior during different stages.
8. When should you create a new component?
When UI part is reusable or has separate logic.
9. Can one component use another component?
Yes, by registering/importing it (Standalone approach: imports: []).
10. What causes "component not known" error?
Component not registered in imports or declarations.
Conclusion
Components form the foundation of every Angular application. By mastering their structure, communication patterns, styling techniques, and lifecycle hooks, you gain the ability to build scalable, maintainable, and dynamic web applications with confidence.
Thank you for reading Mastering Angular Components — From Basics to Advanced
I hope it helped you clearly understand Angular components and their importance in modern application development.