Routing guard

 app.routing.module.ts

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

import { HomeComponent } from './home';
import { LoginComponent } from './login';
import { AuthGuard } from './_helpers';

const routes: Routes = [
    { path: '', component: HomeComponent, canActivate: [AuthGuard] },
    { path: 'login', component: LoginComponent },

    // otherwise redirect to home
    { path: '**', redirectTo: '' }
];

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

auth.guard.ts

import { Injectable } from '@angular/core';
import { Router, CanActivate, ActivatedRouteSnapshot, RouterStateSnapshot } from '@angular/router';

import { AuthenticationService } from '@app/_services';

@Injectable({ providedIn: 'root' })
export class AuthGuard implements CanActivate {
    constructor(
        private router: Router,
        private authenticationService: AuthenticationService
    ) { }

    canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot) {
        const user = this.authenticationService.userValue;
        if (user) {
            // logged in so return true
            return true;
        } else {
            // not logged in so redirect to login page with the return url
            this.router.navigate(['/login'], { queryParams: { returnUrl: state.url } });
            return false;
        }
    }
}

Interceptor example

 app.module.ts

providers: [

    { provide: HTTP_INTERCEPTORS, useClass: JwtInterceptor, multi: true }

]

jwt-interceptor.ts

import { Injectable } from '@angular/core';
import { HttpRequest, HttpHandler, HttpEvent, HttpInterceptor } from '@angular/common/http';
import { Observable } from 'rxjs';

import { environment } from '@environments/environment';
import { AuthenticationService } from '@app/_services';

@Injectable()
export class JwtInterceptor implements HttpInterceptor {
    constructor(private authenticationService: AuthenticationService) { }

    intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        // add auth header with jwt if user is logged in and request is to the api url
        const user = this.authenticationService.userValue;
        const isLoggedIn = user && user.jwtToken;
        const isApiUrl = request.url.startsWith(environment.apiUrl);
        if (isLoggedIn && isApiUrl) {
            request = request.clone({
                setHeaders: { Authorization: `Bearer ${user.jwtToken}` }
            });
        }

        return next.handle(request);
    }
}

Production variables

 environment.ts

export const environment = {
    production: false,
    serviceUrl: "https://localhost:5001"
};

environment.prod.ts

export const environment = {
    production: true,
    serviceUrl: "https://www.site.com"
};

ng build command compiles all project with environment.prod.ts file so if you sure environment.serviceUrl at any point of your code, it will be changed from localhost to site.com...

App Initializer

app.initializer.ts

export function appInitializer(/* authenticationService: AuthenticationService */) {
    return () => new Promise(resolve => {
        console.log("app initialize");
    });
}

app.module.ts

providers: [
    { provide: APP_INITIALIZER, useFactory: appInitializer, multi: true/*, deps: [AuthenticationService]*/ }
],

becareful about the deps and injection parts...