How do AppComponent and @Component relate to each other in AngularJs 2?

Recently, I came across the file app.component.ts in Example and found some interesting code. The link to the example is: here. Here's a snippet of the code:

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

export class Hero {
  id: number;
  name: string;
}

@Component({
  selector: 'my-app',
  template:`
    <h1>{{title}}</h1>
    <h2>{{hero.name}} details!</h2>
    <div><label>id: </label>{{hero.id}}</div>
    <div>
      <label>name: </label>
      <input [(ngModel)]="hero.name" placeholder="name">
    </div>
    `
})
export class AppComponent {
  title = 'Tour of Heroes';
  hero: Hero = {
    id: 1,
    name: 'Windstorm'
  };
}

This code sets the value of title in AppComponent and displays it in the @Component template. This got me thinking - how does this work exactly?

Answer №1

When using the @Component() decorator, it is important to note that it is applied directly to the class, member, or variable following it. This means that in the case of @Component() appearing right before the class AppComponent(), the decorator is specifically targeting this class.

In the context of template: '...', the expressions are evaluated within the scope of the class they are associated with. For example, if we have a reference to title, it will be pointing to the title field within the AppComponent class.

Answer №2

According to Günter, the feature in question functions as a decorator. It's worth noting that the decorator also automatically assigns certain metadata to the related class by utilizing the Reflect Metadata library and executing Reflect.defineMetadata. This metadata corresponds to the parameter specified within the decorator (which is of type ComponentMetadata).

During the component's utilization, Angular2 actively searches for such annotations to determine the appropriate methods for use or configuration of the component.

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