3.属性绑定

//header.component.html
//图片  src要用中括号括起来
<img [src]="imageUrl" alt="">   
//header.component.ts
export class HeaderComponent implements OnInit {
  public imageUrl:string="https://c-ssl.duitang.com/uploads/item/201912/02/20191202100553_HPUuW.thumb.700_0.jpeg"
  constructor() { }
  ngOnInit() {
  }
}