Component Pattern

In Angular, the Component Pattern is a fundamental concept that revolves around building applications by composing them from smaller, reusable, and self-contained building blocks called components.

Each component encapsulates a specific functionality, user interface, or behavior.

Here's a breakdown of the Component Pattern in Angular along with a simple code example:

1. Component Definition: Components are defined using the @Component decorator in Angular. This decorator provides metadata about the component such as its selector, template, styles, etc.

import { Component } from '@angular/core';

@Component({
  selector: 'app-example', // Selector for using this component in other templates
  template: `
    <div>
      <h2>Hello, {{ name }}!</h2>
      <button (click)="changeName()">Change Name</button>
    </div>
  `, // Template for the component
  styles: [`h2 { color: blue; }`] // Styles for the component
})
export class ExampleComponent {
  name: string = 'World';

  changeName() {
    this.name = 'Angular';
  }
}

1. Component Composition: Components can be composed together to form complex user interfaces. They can be nested within each other to create a tree-like structure.

import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  template: `
    <div>
      <app-example></app-example>
    </div>
  `
})
export class AppComponent {}

In this example, the AppComponent includes the ExampleComponent by using its selector <app-example></app-example>.

1. Reusability: Components promote reusability since they are self-contained units. They can be reused across different parts of the application or even in different applications altogether.

2. Encapsulation: Each component encapsulates its own logic, styles, and template, which helps in maintaining the codebase and makes it easier to reason about.

3. Communication between Components: Components can communicate with each other using various techniques such as Input/Output properties, ViewChild/ContentChild, services, or even event emitters.

import { Component, Input } from '@angular/core';

@Component({
  selector: 'app-child',
  template: `
    <div>
      <h3>Child Component</h3>
      <p>Received message: {{ message }}</p>
    </div>
  `
})
export class ChildComponent {
  @Input() message: string;
}

In this example, the ChildComponent receives a message from its parent component using an input property message.

Overall, the Component Pattern in Angular helps in building scalable, maintainable, and modular applications by breaking down the user interface into reusable and manageable components.