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The Core Concept:
Angular Components

Learn how to build modular, reusable user interfaces. Understand the relationship between the Class, the Template, and the Decorator.

Lesson ProgressStep 1 of 7
Visualizing Component Structure...
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Welcome! Let's dissect an Angular Component. It's the heart of any Angular application, combining logic, structure, and style.

// Initializing Component Simulator...

The TypeScript Class

Every component starts as a standard TypeScript class. This is where you define the behavior of your view. Properties (variables) hold state, and methods (functions) handle events like button clicks.

export class HelloComponent {
  name: string = 'Angular';
  
  sayHello() {
    alert('Hello ' + this.name);
  }
}

System Check

Where does the logical behavior (methods and properties) of a component live?

Advanced Holo-Simulations

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Aplica tus conocimientos en estas simulaciones avanzadas. ¡Todo nuestro contenido es gratuito!

Achievements

🛡️
Decorator Master

Successfully define component metadata using @Component.

🏗️
Template Architect

Correctly structure the component class and template link.

🔄
Lifecycle Learner

Demonstrate knowledge of component initialization.

Mission: Construct a Component

Write a basic Angular component structure. You need the decorator, a selector, a template, and the exported class.

A.D.A. Feedback:

> Awaiting input...

Challenge: Component File Structure

Drag the code blocks into the correct order for a valid TypeScript component file.

@Component({...})
import { Component } from '@angular/core';
export class AppComponent {}

Challenge: Metadata Properties

Fill in the missing properties of the @Component decorator.

@Component({
: 'app-header',
: './header.component.html',
: ['./header.component.css']
})

Consult A.D.A. (Angular Digital Assistant)

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Community Holo-Net

Peer Project Review

Submit your "User Card Component" for feedback from other Angular developers.

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Beyond the Basics: The Angular Component Ecosystem

Understanding the syntax of an Angular component is just the first step. To truly master the framework, you must understand how components interact, encapsulate styles, and manage their own lifecycle.

View Encapsulation: The Shadow DOM

One of Angular's most powerful features is **View Encapsulation**. By default, CSS defined in a component's `styleUrls` file does not leak out to the rest of the application, nor do global styles easily bleed in.

Angular achieves this by emulating the Shadow DOM. It automatically attaches unique attributes (like `_ngcontent-c1`) to your HTML elements and modifies your CSS selectors to match only those attributes. This means you can use generic class names like `.card` in every component without fear of collision.

Data Binding and Interaction

Components rarely exist in isolation. They communicate via a strict API:

⬇️ Input (Props)

@Input() userData: User;

Data flows *down* from parent to child using property binding `[userData]="user"`.

⬆️ Output (Events)

@Output() onSave = new EventEmitter();

Events flow *up* from child to parent using event binding `(onSave)="save($event)"`.

Lifecycle Hooks

Angular gives you visibility into key moments of a component's life. The most common hook is `ngOnInit`.

Best Practice: Never fetch data inside the `constructor`. The constructor is for JavaScript class initialization (Dependency Injection). Use `ngOnInit` for Angular-specific setup logic like API calls.

Angular Components Glossary

Component
The fundamental building block of an Angular application, controlling a view (a patch of screen). It combines a TS class with an HTML template.
Decorator (@Component)
A function that adds metadata to a class, instructing Angular how to compile and use it.
Selector
A CSS selector that identifies this component in a template. Commonly used as an element tag (e.g., `<app-home>`).
Template
The HTML view for the component. It can be inline (in the decorator) or an external file (`templateUrl`).
Interpolation
One-way data binding from the class to the template, denoted by double curly braces `{{ value }}`.
Lifecycle Hooks
Interfaces (like `OnInit`, `OnDestroy`) that allow you to tap into specific moments in a component's existence.
Shadow DOM
A web standard that Angular emulates to scope CSS styles so they don't leak outside of the component.

About the Author

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TodoTutorial Team

Passionate developers and educators making programming accessible to everyone.

This article was written and reviewed by our team of web development experts, who have years of experience building enterprise applications with Angular.

Verification and Updates

Last reviewed: October 2025.

We strive to keep our content accurate and up-to-date. This tutorial is based on Angular v18+ specifications.

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