@Component({
  selector: 'my-app',
  template: `
    <ul>
     <li *ngFor="let letter of letters">
      {{letter}}
     </li>
    </ul>
  `,
})
export class App {
  constructor() {
    this.letters = {
      0: 'a',
      1: 'b',
      2: 'c',
      length: 3,
      [Symbol.iterator]() {
        let index = 0;
        return {
            next: () => {
                let value = this[index];
                let done = index >= this.length;
                index++;
                return { value, done };
            }
        };
      }
    };
  }
}