Angular `<router-outlet>` displays template twice

Your default route points to AppComponent, so your route is rendering the AppComponent inside the AppComponent.

Create a DashboardComponent or HomeComponent for this. And then do:

{ path: '', component: DashboardComponent }

Update 1:

As @GünterZöchbauer mentioned, we should add pathMatch: 'full' for "an empty path route with no children".

So we can go with the AppComponent approach (check Günter's answer):

{ path: '', component: AppComponent, pathMatch: 'full' }

Or, the DashboardComponent approach as I stated above in my answer.

Why is this happening?

1) In your application entry point, most likely main.ts, one can read this line:

platformBrowserDynamic().bootstrapModule(AppModule);

This tells angular to bootstrap the module AppModule

2) In AppModule, one can find this line:

bootstrap: [ AppComponent ]

This tells angular to bootstrap the component AppComponent. This is why you see the first Contacts App part, because the html template of the AppComponent is:

<h1>Contacts App</h1>
<ul>
    <li><a [routerLink]="['/facebook/top']">Contact List</a></li>
</ul>
<router-outlet></router-outlet>

3) However, the template of your AppComponent also contains <router-outlet>. The router reads the routes configuration, accordingly creates a new instance of AppComponent and inject it right after the element <router-outlet>. This is why you see the second Contacts App part.