在angular 4中切换routeLink

import { RouterModule, Routes } from '@angular/router';

const routes: Routes = [
  { path: 'home', component: HomeComponent },
  { path: 'about', component: AboutComponent },
  { path: 'contact', component: ContactComponent },
];

@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule]
})
export class AppModule { }

<a routerLink="/home">Home</a>
<a routerLink="/about">About</a>
<a routerLink="/contact">Contact</a>

<a [routerLink]="['/user', userId]">User Profile</a>

<a routerLink="/home" routerLinkActive="active">Home</a>
<a routerLink="/about" routerLinkActive="active">About</a>
<a routerLink="/contact" routerLinkActive="active">Contact</a>