Router Reference

The following sections highlight some core router concepts.

Router imports

The Angular Router is an optional service that presents a particular component view for a given URL. It is not part of the Angular core and thus is in its own library package, @angular/router.

Import what you need from it as you would from any other Angular package.

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

For more on browser URL styles, see LocationStrategy and browser URL styles.

Configuration

A routed Angular application has one singleton instance of the Router service. When the browser's URL changes, that router looks for a corresponding Route from which it can determine the component to display.

A router has no routes until you configure it. The following example creates five route definitions, configures the router via the RouterModule.forRoot() method, and adds the result to the AppModule's imports array.

const appRoutes: Routes = [
  { path: 'crisis-center', component: CrisisListComponent },
  { path: 'hero/:id',      component: HeroDetailComponent },
  {
    path: 'heroes',
    component: HeroListComponent,
    data: { title: 'Heroes List' }
  },
  { path: '',
    redirectTo: '/heroes',
    pathMatch: 'full'
  },
  { path: '**', component: PageNotFoundComponent }
];

@NgModule({
  imports: [
    RouterModule.forRoot(
      appRoutes,
      { enableTracing: true } // <-- debugging purposes only
    )
    // other imports here
  ],
  ...
})
export class AppModule { }

The appRoutes array of routes describes how to navigate. Pass it to the RouterModule.forRoot() method in the module imports to configure the router.

Each Route maps a URL path to a component. There are no leading slashes in the path. The router parses and builds the final URL for you, which lets you use both relative and absolute paths when navigating between application views.

The :id in the second route is a token for a route parameter. In a URL such as /hero/42, "42" is the value of the id parameter. The corresponding HeroDetailComponent uses that value to find and present the hero whose id is 42.

The data property in the third route is a place to store arbitrary data associated with this specific route. The data property is accessible within each activated route. Use it to store items such as page titles, breadcrumb text, and other read-only, static data. Use the resolve guard to retrieve dynamic data.

The empty path in the fourth route represents the default path for the application—the place to go when the path in the URL is empty, as it typically is at the start. This default route redirects to the route for the /heroes URL and, therefore, displays the HeroesListComponent.

If you need to see what events are happening during the navigation lifecycle, there is the enableTracing option as part of the router's default configuration. This outputs each router event that took place during each navigation lifecycle to the browser console. Use enableTracing only for debugging purposes. You set the enableTracing: true option in the object passed as the second argument to the RouterModule.forRoot() method.

Router outlet

The RouterOutlet is a directive from the router library that is used like a component. It acts as a placeholder that marks the spot in the template where the router should display the components for that outlet.

<router-outlet></router-outlet>
  <!-- Routed components go here -->

Given the preceding configuration, when the browser URL for this application becomes /heroes, the router matches that URL to the route path /heroes and displays the HeroListComponent as a sibling element to the RouterOutlet that you've placed in the host component's template.

Router links

To navigate as a result of some user action such as the click of an anchor tag, use RouterLink.

Consider the following template:

<h1>Angular Router</h1>
<nav>
  <a routerLink="/crisis-center" routerLinkActive="active">Crisis Center</a>
  <a routerLink="/heroes" routerLinkActive="active">Heroes</a>
</nav>
<router-outlet></router-outlet>

The RouterLink directives on the anchor tags give the router control over those elements. The navigation paths are fixed, so you can assign a string to the routerLink (a "one-time" binding).

Had the navigation path been more dynamic, you could have bound to a template expression that returned an array of route link parameters; that is, the link parameters array. The router resolves that array into a complete URL.

Active router links

The RouterLinkActive directive toggles CSS classes for active RouterLink bindings based on the current RouterState.

On each anchor tag, you see a property binding to the RouterLinkActive directive that looks like routerLinkActive="...".

The template expression to the right of the equal sign, =, contains a space-delimited string of CSS classes that the Router adds when this link is active (and removes when the link is inactive). You set the RouterLinkActive directive to a string of classes such as routerLinkActive="active fluffy" or bind it to a component property that returns such a string (for example, [routerLinkActive]="someStringProperty").

Active route links cascade down through each level of the route tree, so parent and child router links can be active at the same time. To override this behavior, bind to the [routerLinkActiveOptions] input binding with the { exact: true } expression. By using { exact: true }, a given RouterLink is only active if its URL is an exact match to the current URL.

Router state

After the end of each successful navigation lifecycle, the router builds a tree of ActivatedRoute objects that make up the current state of the router. You can access the current RouterState from anywhere in the application using the Router service and the routerState property.

Each ActivatedRoute in the RouterState provides methods to traverse up and down the route tree to get information from parent, child, and sibling routes.

Activated route

The route path and parameters are available through an injected router service called the ActivatedRoute. It has a great deal of useful information including:

Property	Description
url	An Observable of the route path(s), represented as an array of strings for each part of the route path.
data	An Observable that contains the data object provided for the route. Also contains any resolved values from the resolve guard.
params	An Observable that contains the required and optional parameters specific to the route.
paramMap	An Observable that contains a map of the required and optional parameters specific to the route. The map supports retrieving single and multiple values from the same parameter.
queryParamMap	An Observable that contains a map of the query parameters available to all routes. The map supports retrieving single and multiple values from the query parameter.
queryParams	An Observable that contains the query parameters available to all routes.
fragment	An Observable of the URL fragment available to all routes.
outlet	The name of the RouterOutlet used to render the route. For an unnamed outlet, the outlet name is primary.
routeConfig	The route configuration used for the route that contains the origin path.
parent	The route's parent ActivatedRoute when this route is a child route.
firstChild	Contains the first ActivatedRoute in the list of this route's child routes.
children	Contains all the child routes activated under the current route.

Router events

During each navigation, the Router emits navigation events through the Router.events property. These events range from when the navigation starts and ends to many points in between. The full list of navigation events is displayed in the following table.

Router Event	Description
NavigationStart	An event triggered when navigation starts.
RouteConfigLoadStart	An event triggered before the Router lazy loads a route configuration.
RouteConfigLoadEnd	An event triggered after a route has been lazy loaded.
RoutesRecognized	An event triggered when the Router parses the URL and the routes are recognized.
GuardsCheckStart	An event triggered when the Router begins the Guards phase of routing.
ChildActivationStart	An event triggered when the Router begins activating a route's children.
ActivationStart	An event triggered when the Router begins activating a route.
GuardsCheckEnd	An event triggered when the Router finishes the Guards phase of routing successfully.
ResolveStart	An event triggered when the Router begins the Resolve phase of routing.
ResolveEnd	An event triggered when the Router finishes the Resolve phase of routing successfuly.
ChildActivationEnd	An event triggered when the Router finishes activating a route's children.
ActivationEnd	An event triggered when the Router finishes activating a route.
NavigationEnd	An event triggered when navigation ends successfully.
NavigationCancel	An event triggered when navigation is canceled. This can happen when a Route Guard returns false during navigation, or redirects by returning a UrlTree.
NavigationError	An event triggered when navigation fails due to an unexpected error.
Scroll	An event that represents a scrolling event.

When you enable the enableTracing option, Angular logs these events to the console. For an example of filtering router navigation events, see the router section of the Observables in Angular guide.

Router terminology

Here are the key Router terms and their meanings:

Router Part	Meaning
Router	Displays the application component for the active URL. Manages navigation from one component to the next.
RouterModule	A separate NgModule that provides the necessary service providers and directives for navigating through application views.
Routes	Defines an array of Routes, each mapping a URL path to a component.
Route	Defines how the router should navigate to a component based on a URL pattern. Most routes consist of a path and a component type.
RouterOutlet	The directive (<router-outlet>) that marks where the router displays a view.
RouterLink	The directive for binding a clickable HTML element to a route. Clicking an element with a routerLink directive that is bound to a string or a link parameters array triggers a navigation.
RouterLinkActive	The directive for adding/removing classes from an HTML element when an associated routerLink contained on or inside the element becomes active/inactive.
ActivatedRoute	A service that is provided to each route component that contains route specific information such as route parameters, static data, resolve data, global query params, and the global fragment.
RouterState	The current state of the router including a tree of the currently activated routes together with convenience methods for traversing the route tree.
Link parameters array	An array that the router interprets as a routing instruction. You can bind that array to a RouterLink or pass the array as an argument to the Router.navigate method.
Routing component	An Angular component with a RouterOutlet that displays views based on router navigations.