app.component.ts

import { Component } from '@angular/core';
@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'pinduoduo';
  tabs = ['x', 'y']
}

app.component.html

<ul>
  <li *ngFor="let item of tabs"><a href="#">{{ item }}</a></li>
</ul>

模板+样式+元数据= 组件