如何在angular2中高亮显示导航栏？

<ul>
  <li [ngClass]="{'active': isActive('/home')}"><a routerLink="/home">Home</a></li>
  <li [ngClass]="{'active': isActive('/about')}"><a routerLink="/about">About</a></li>
  <li [ngClass]="{'active': isActive('/contact')}"><a routerLink="/contact">Contact</a></li>
</ul>

import { Router } from '@angular/router';

export class NavbarComponent {
  constructor(private router: Router) {}

  isActive(route: string): boolean {
    return this.router.url === route;
  }
}

.active {
  background-color: yellow;
}