function Show(props: ShowProps): DocumentFragment;

@Component
class RouteView extends BaseComponent {
  @Resource(...)
  componentClass!: IResource<any>;
  
  view() {
    return (
      <>
        <Show when={() => this.componentClass.state === 'pending'}>
          {() => <div>Loading...</div>}
        </Show>
        
        <Show when={() => this.componentClass.state === 'ready'}>
          {() => this.jsx(this.componentClass.get(), {})}
        </Show>
      </>
    );
  }
}

<Show 
  when={() => this.user.isLoggedIn}
  fallback={() => <LoginButton />}
>
  {() => <UserProfile user={this.user} />}
</Show>