Angular2: Export of RouterModule, Why it is required?

Question

I am learning Angular 2's app-routing from official documentation. I am going through following piece of code.

import { NgModule }             from '@angular/core'; import { Routes, RouterModule } from '@angular/router';  export const routes: Routes = [   { path: '', redirectTo: 'contact', pathMatch: 'full'},   { path: 'crisis', loadChildren: 'app/crisis/crisis.module#CrisisModule' },   { path: 'heroes', loadChildren: 'app/hero/hero.module#HeroModule' } ];  @NgModule({   imports: [RouterModule.forRoot(routes)],   exports: [RouterModule] }) export class AppRoutingModule {} 

It creates an AppRoutingModule and defines routes for it. The part which I am not able to understand is Why do we need to export RouterModule again? I believe it's one of the core angular module and which available everywhere by import of @angular/router.

Answer 1

You don't need to export it. It's just for convenience. If you add AppRoutingModule to AppModule you also implicitly import RouterModule this way. Otherwise you would need to import it explicitely

@NgModule({   imports: [AppRoutingModule, RouterModule], }) export class AppModule {} 

for example to be able to use <router-outlet> or RouterLink in components declared in AppModule

Answer 2

Do you need a Routing Module?

The Routing Module replaces the routing configuration in the root or feature module. Either configure routes in the Routing Module or within the module itself but not in both.

The Routing Module is a design choice whose value is most obvious when the configuration is complex and includes specialized guard and resolver services. It can seem like overkill when the actual configuration is dead simple.

Some developers skip the Routing Module (for example, AppRoutingModule) when the configuration is simple and merge the routing configuration directly into the companion module (for example, AppModule).

Choose one pattern or the other and follow that pattern consistently.

Most developers should always implement a Routing Module for the sake of consistency. It keeps the code clean when configuration becomes complex. It makes testing the feature module easier. Its existence calls attention to the fact that a module is routed. It is where developers expect to find and expand routing configuration.