The Angular Router enables navigation from one view to the next
as users perform application tasks.
This guide covers the router's primary features, illustrating them through the evolution
of a small application that you can run live in the browserrun live in the browser / download example.
The browser is a familiar model of application navigation:
Enter a URL in the address bar and the browser navigates to a corresponding page.
Click links on the page and the browser navigates to a new page.
Click the browser's back and forward buttons and the browser navigates
backward and forward through the history of pages you've seen.
The Angular Router ("the router") borrows from this model.
It can interpret a browser URL as an instruction to navigate to a client-generated view.
It can pass optional parameters along to the supporting view component that help it decide what specific content to present.
You can bind the router to links on a page and it will navigate to
the appropriate application view when the user clicks a link.
You can navigate imperatively when the user clicks a button, selects from a drop box,
or in response to some other stimulus from any source. And the router logs activity
in the browser's history journal so the back and forward buttons work as well.
This guide proceeds in phases, marked by milestones, starting from a simple two-pager
and building toward a modular, multi-view design with child routes.
An introduction to a few core router concepts will help orient you to the details that follow.
Most routing applications should add a <base> element to the index.html as the first child in the <head> tag
to tell the router how to compose navigation URLs.
If the app folder is the application root, as it is for the sample application,
set the href value exactly as shown here.
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. It is in its own library package, @angular/router.
Import what you need from it as you would from any other Angular package.
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.
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,
allowing you to 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
will use that value to find and present the hero whose id is 42.
You'll learn more about route parameters later in this guide.
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.
You'll use the resolve guard to retrieve dynamic data later in the guide.
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, will display the HeroesListComponent.
The ** path in the last route is a wildcard. The router will select this route
if the requested URL doesn't match any paths for routes defined earlier in the configuration.
This is useful for displaying a "404 - Not Found" page or redirecting to another route.
The order of the routes in the configuration matters and this is by design. The router uses a first-match wins
strategy when matching routes, so more specific routes should be placed above less specific routes.
In the configuration above, routes with a static path are listed first, followed by an empty path route,
that matches the default route.
The wildcard route comes last because it matches every URL and should be selected only if no other routes are matched first.
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. This should only be used for debugging purposes. You set the enableTracing: true option in the object passed as the second argument to the RouterModule.forRoot() method.
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.
Given the configuration above, 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.
Now you have routes configured and a place to render them, but
how do you navigate? The URL could arrive directly from the browser address bar.
But most of the time you navigate as a result of some user action such as the click of
an anchor tag.
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 (the link parameters array).
The router resolves that array into a complete URL.
The template expression to the right of the equals (=) contains a space-delimited string of CSS classes
that the Router will add when this link is active (and remove 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.
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, you can bind to the [routerLinkActiveOptions] input binding with the { exact: true } expression. By using { exact: true }, a given RouterLink will only be active if its URL is an exact match to the current URL.
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.
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.
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.
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.
Contains the first ActivatedRoute in the list of this route's child routes.
children
Contains all the child routes activated under the current route.
Two older properties are still available. They are less capable than their replacements, discouraged, and may be deprecated in a future Angular version.
params—An Observable that contains the required and optional parameters specific to the route. Use paramMap instead.
queryParams—An Observable that contains the query parameters available to all routes.
Use queryParamMap instead.
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 table below.
These events are logged to the console when the enableTracing option is enabled also. For an example of filtering router navigation events, visit the router section of the Observables in Angular guide.
The application has a configured router.
The shell component has a RouterOutlet where it can display views produced by the router.
It has RouterLinks that users can click to navigate via the router.
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.
The directive for adding/removing classes from an HTML element when an associated
routerLink contained on or inside the element becomes active/inactive.
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.
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.
This guide describes development of a multi-page routed sample application.
Along the way, it highlights design decisions and describes key features of the router such as:
Organizing the application features into modules.
Navigating to a component (Heroes link to "Heroes List").
Including a route parameter (passing the Hero id while routing to the "Hero Detail").
Child routes (the Crisis Center has its own routes).
The CanLoad guard (check before loading feature module assets).
The guide proceeds as a sequence of milestones as if you were building the app step-by-step.
But, it is not a tutorial and it glosses over details of Angular application construction
that are more thoroughly covered elsewhere in the documentation.
The full source for the final version of the app can be seen and downloaded from the live example / download example.
Once the app warms up, you'll see a row of navigation buttons
and the Heroes view with its list of heroes.
Select one hero and the app takes you to a hero editing screen.
Alter the name.
Click the "Back" button and the app returns to the heroes list which displays the changed hero name.
Notice that the name change took effect immediately.
Had you clicked the browser's back button instead of the "Back" button,
the app would have returned you to the heroes list as well.
Angular app navigation updates the browser history as normal web navigation does.
Now click the Crisis Center link for a list of ongoing crises.
Select a crisis and the application takes you to a crisis editing screen.
The Crisis Detail appears in a child component on the same page, beneath the list.
Alter the name of a crisis.
Notice that the corresponding name in the crisis list does not change.
Unlike Hero Detail, which updates as you type,
Crisis Detail changes are temporary until you either save or discard them by pressing the "Save" or "Cancel" buttons.
Both buttons navigate back to the Crisis Center and its list of crises.
Do not click either button yet.
Click the browser back button or the "Heroes" link instead.
Up pops a dialog box.
You can say "OK" and lose your changes or click "Cancel" and continue editing.
Behind this behavior is the router's CanDeactivate guard.
The guard gives you a chance to clean-up or ask the user's permission before navigating away from the current view.
The Admin and Login buttons illustrate other router capabilities to be covered later in the guide.
This short introduction will do for now.
A router must be configured with a list of route definitions.
Each definition translates to a Route object which has two things: a
path, the URL path segment for this route; and a
component, the component associated with this route.
The router draws upon its registry of definitions when the browser URL changes
or when application code tells the router to navigate along a route path.
In simpler terms, you might say this of the first route:
When the browser's location URL changes to match the path segment /crisis-center, then
the router activates an instance of the CrisisListComponent and displays its view.
When the application requests navigation to the path /crisis-center, the router
activates an instance of CrisisListComponent, displays its view, and updates the
browser's address location and history with the URL for that path.
The first configuration defines an array of two routes with simple paths leading to the
CrisisListComponent and HeroListComponent. Generate the CrisisList and HeroList components.
ng generate component crisis-list
ng generate component crisis-list
ng generate component hero-list
ng generate component hero-list
Replace the contents of each component with the sample HTML below.
<h2>CRISIS CENTER</h2>
<p>Get your crisis here</p>
<h2>HEROES</h2>
<p>Get your heroes here</p>
In order to use the Router, you must first register the RouterModule from the @angular/router package. Define an array of routes, appRoutes, and pass them to the RouterModule.forRoot() method. It returns a module, containing the configured Router service provider, plus other providers that the routing library requires. Once the application is bootstrapped, the Router performs the initial navigation based on the current browser URL.
Note: The RouterModule.forRoot method is a pattern used to register application-wide providers. Read more about application-wide providers in the Singleton services guide.
Adding the configured RouterModule to the AppModule is sufficient for simple route configurations. As the application grows, you'll want to refactor the routing configuration into a separate file and create a Routing Module, a special type of Service Module dedicated to the purpose of routing in feature modules.
Registering the RouterModule.forRoot() in the AppModule imports makes the Router service available everywhere in the application.
The root AppComponent is the application shell. It has a title, a navigation bar with two links, and a router outlet where the router swaps components on and off the page. Here's what you get:
The router outlet serves as a placeholder when the routed components will be rendered below it.
The corresponding component template looks like this:
You've created two routes in the app so far, one to /crisis-center and the other to /heroes. Any other URL causes the router to throw an error and crash the app.
Add a wildcard route to intercept invalid URLs and handle them gracefully.
A wildcard route has a path consisting of two asterisks. It matches every URL.
The router will select this route if it can't match a route earlier in the configuration.
A wildcard route can navigate to a custom "404 Not Found" component or redirect to an existing route.
The router selects the route with a first match wins strategy.
Wildcard routes are the least specific routes in the route configuration.
Be sure it is the last route in the configuration.
To test this feature, add a button with a RouterLink to the HeroListComponent template and set the link to "/sidekicks".
<h2>HEROES</h2>
<p>Get your heroes here</p>
<button routerLink="/sidekicks">Go to sidekicks</button>
Now when the user visits /sidekicks, or any other invalid URL, the browser displays "Page not found".
The browser address bar continues to point to the invalid URL.
When the application launches, the initial URL in the browser bar is something like:
localhost:4200
localhost:4200
That doesn't match any of the concrete configured routes which means
the router falls through to the wildcard route and displays the PageNotFoundComponent.
The application needs a default route to a valid page.
The default page for this app is the list of heroes.
The app should navigate there as if the user clicked the "Heroes" link or pasted localhost:4200/heroes into the address bar.
The preferred solution is to add a redirect route that translates the initial relative URL ('')
to the desired default path (/heroes). The browser address bar shows .../heroes as if you'd navigated there directly.
Add the default route somewhere above the wildcard route.
It's just above the wildcard route in the following excerpt showing the complete appRoutes for this milestone.
A redirect route requires a pathMatch property to tell the router how to match a URL to the path of a route.
The router throws an error if you don't.
In this app, the router should select the route to the HeroListComponent only when the entire URL matches '',
so set the pathMatch value to 'full'.
Technically, pathMatch = 'full' results in a route hit when the remaining, unmatched segments of the URL match ''.
In this example, the redirect is in a top level route so the remaining URL and the entire URL are the same thing.
The other possible pathMatch value is 'prefix' which tells the router
to match the redirect route when the remaining URL begins with the redirect route's prefix path.
Don't do that here.
If the pathMatch value were 'prefix', every URL would match ''.
Try setting it to 'prefix' then click the Go to sidekicks button.
Remember that's a bad URL and you should see the "Page not found" page.
Instead, you're still on the "Heroes" page.
Enter a bad URL in the browser address bar.
You're instantly re-routed to /heroes.
Every URL, good or bad, that falls through to this route definition
will be a match.
The default route should redirect to the HeroListComponentonly when the entire url is ''.
Remember to restore the redirect to pathMatch = 'full'.
In the initial route configuration, you provided a simple setup with two routes used
to configure the application for routing. This is perfectly fine for simple routing.
As the application grows and you make use of more Router features, such as guards,
resolvers, and child routing, you'll naturally want to refactor the routing configuration into its own file.
We recommend moving the routing information into a special-purpose module called a Routing Module.
The Routing Module has several characteristics:
Separates routing concerns from other application concerns.
Provides a module to replace or remove when testing the application.
Provides a well-known location for routing service providers including guards and resolvers.
The sample routing application does not include routing by default.
When you use the CLI to create a project that will use routing, set the --routing option for the project or app, and for each NgModule.
When you create or initialize a new project (using the CLI new command) or a new app (using the generate app command), specify the --routing option. This tells the CLI to include the @angular/router npm package and create a file named app-routing.module.ts.
You can then use routing in any NgModule that you add to the project or app.
For example, the following command generates an NgModule that can use routing.
ng generate module my-module --routing
ng generate module my-module --routing
This creates a separate file named my-module-routing.module.ts to store the NgModule's routes.
The file includes an empty Routes object that you can fill with routes to different components and NgModules.
Refactor the routing configuration into a routing modulelink
Create an AppRouting module in the /app folder to contain the routing configuration.
ng generate module app-routing --module app --flat
ng generate module app-routing --module app --flat
Import the CrisisListComponent, HeroListComponent, and PageNotFoundCompponent symbols
just like you did in the app.module.ts. Then move the Router imports
and routing configuration, including RouterModule.forRoot, into this routing module.
Re-export the Angular RouterModule by adding it to the module exports array.
By re-exporting the RouterModule here the components declared in AppModule will have access to router directives such as RouterLink and RouterOutlet.
After these steps, the file should look like this.
The Routing Modulereplaces 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.
Here's how the user will experience this version of the app:
A typical application has multiple feature areas,
each dedicated to a particular business purpose.
While you could continue to add files to the src/app/ folder,
that is unrealistic and ultimately not maintainable.
Most developers prefer to put each feature area in its own folder.
You are about to break up the app into different feature modules, each with its own concerns.
Then you'll import into the main module and navigate among them.
Create a HeroesModule with routing in the heroes folder and register it with the root AppModule. This is where you'll be implementing the hero management.
ng generate module heroes/heroes --module app --flat --routing
ng generate module heroes/heroes --module app --flat --routing
Move the placeholder hero-list folder that's in the app into the heroes folder.
Copy the contents of the heroes/heroes.component.html from
the "Services" tutorial"Services" tutorial / download example into the hero-list.component.html template.
Relabel the <h2> to <h2>HEROES</h2>.
Delete the <app-hero-detail> component at the bottom of the template.
Copy the contents of the heroes/heroes.component.css from the live example into the hero-list.component.css file.
Copy the contents of the heroes/heroes.component.ts from the live example into the hero-list.component.ts file.
Change the component class name to HeroListComponent.
Change the selector to app-hero-list.
Selectors are not required for routed components due to the components are dynamically inserted when the page is rendered, but are useful for identifying and targeting them in your HTML element tree.
Copy the hero-detail folder, the hero.ts, hero.service.ts, and mock-heroes.ts files into the heroes subfolder.
Copy the message.service.ts into the src/app folder.
Update the relative path import to the message.service in the hero.service.ts file.
Next, you'll update the HeroesModule metadata.
Import and add the HeroDetailComponent and HeroListComponent to the declarations array in the HeroesModule.
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { FormsModule } from '@angular/forms';
import { HeroListComponent } from './hero-list/hero-list.component';
import { HeroDetailComponent } from './hero-detail/hero-detail.component';
import { HeroesRoutingModule } from './heroes-routing.module';
@NgModule({
imports: [
CommonModule,
FormsModule,
HeroesRoutingModule
],
declarations: [
HeroListComponent,
HeroDetailComponent
]
})
export class HeroesModule {}
The heroes feature has two interacting components, the hero list and the hero detail.
The list view is self-sufficient; you navigate to it, it gets a list of heroes and displays them.
The detail view is different. It displays a particular hero. It can't know which hero to show on its own.
That information must come from outside.
When the user selects a hero from the list, the app should navigate to the detail view
and show that hero.
You tell the detail view which hero to display by including the selected hero's id in the route URL.
Import the hero components from their new locations in the src/app/heroes/ folder, define the two hero routes.
Now that you have routes for the Heroes module, register them with the Router via the
RouterModulealmost as you did in the AppRoutingModule.
There is a small but critical difference.
In the AppRoutingModule, you used the static RouterModule.forRoot method to register the routes and application level service providers.
In a feature module you use the static forChild method.
Only call RouterModule.forRoot in the root AppRoutingModule
(or the AppModule if that's where you register top level application routes).
In any other module, you must call the RouterModule.forChild method to register additional routes.
Consider giving each feature module its own route configuration file.
It may seem like overkill early when the feature routes are simple.
But routes have a tendency to grow more complex and consistency in patterns pays off over time.
The hero routes are currently defined in two places: in the HeroesRoutingModule,
by way of the HeroesModule, and in the AppRoutingModule.
Routes provided by feature modules are combined together into their imported module's routes by the router.
This allows you to continue defining the feature module routes without modifying the main route configuration.
Remove the HeroListComponent import and the /heroes route from the app-routing.module.ts.
Leave the default and the wildcard routes!
These are concerns at the top level of the application itself.
import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { CrisisListComponent } from './crisis-list/crisis-list.component';
// import { HeroListComponent } from './hero-list/hero-list.component'; // <-- delete this line
import { PageNotFoundComponent } from './page-not-found/page-not-found.component';
const appRoutes: Routes = [
{ path: 'crisis-center', component: CrisisListComponent },
// { path: 'heroes', component: HeroListComponent }, // <-- delete this line
{ path: '', redirectTo: '/heroes', pathMatch: 'full' },
{ path: '**', component: PageNotFoundComponent }
];
@NgModule({
imports: [
RouterModule.forRoot(
appRoutes,
{ enableTracing: true } // <-- debugging purposes only
)
],
exports: [
RouterModule
]
})
export class AppRoutingModule {}
Remove the HeroListComponent from the AppModule's declarations because it's now provided by the HeroesModule. You can evolve the hero feature with more components and different routes. That's a key benefit of creating a separate module for each feature area.
After these steps, the AppModule should look like this:
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule } from '@angular/forms';
import { AppComponent } from './app.component';
import { AppRoutingModule } from './app-routing.module';
import { HeroesModule } from './heroes/heroes.module';
import { CrisisListComponent } from './crisis-list/crisis-list.component';
import { PageNotFoundComponent } from './page-not-found/page-not-found.component';
@NgModule({
imports: [
BrowserModule,
FormsModule,
HeroesModule,
AppRoutingModule
],
declarations: [
AppComponent,
CrisisListComponent,
PageNotFoundComponent
],
bootstrap: [ AppComponent ]
})
export class AppModule { }
The order of route configuration matters.
The router accepts the first route that matches a navigation request path.
When all routes were in one AppRoutingModule,
you put the default and wildcard routes last, after the /heroes route,
so that the router had a chance to match a URL to the /heroes route before
hitting the wildcard route and navigating to "Page not found".
The routes are no longer in one file.
They are distributed across two modules, AppRoutingModule and HeroesRoutingModule.
Each routing module augments the route configuration in the order of import.
If you list AppRoutingModule first, the wildcard route will be registered
before the hero routes.
The wildcard route—which matches every URL—will intercept the attempt to navigate to a hero route.
Reverse the routing modules and see for yourself that
a click of the heroes link results in "Page not found".
Learn about inspecting the runtime router configuration
below.
Notice the :id token in the path. That creates a slot in the path for a Route Parameter.
In this case, the router will insert the id of a hero into that slot.
If you tell the router to navigate to the detail component and display "Magneta",
you expect a hero id to appear in the browser URL like this:
localhost:4200/hero/15
localhost:4200/hero/15
If a user enters that URL into the browser address bar, the router should recognize the
pattern and go to the same "Magneta" detail view.
Route parameter: Required or optional?
Embedding the route parameter token, :id,
in the route definition path is a good choice for this scenario
because the id is required by the HeroDetailComponent and because
the value 15 in the path clearly distinguishes the route to "Magneta" from
a route for some other hero.
After navigating to the HeroDetailComponent, you expect to see the details of the selected hero.
You need two pieces of information: the routing path to the component and the hero's id.
Accordingly, the link parameters array has two items: the routing path and a route parameter that specifies the
id of the selected hero.
Later, in the ngOnInit method, you use the ActivatedRoute service to retrieve the parameters for the route,
pull the hero id from the parameters and retrieve the hero to display.
The paramMap processing is a bit tricky. When the map changes, you get()
the id parameter from the changed parameters.
Then you tell the HeroService to fetch the hero with that id and return the result of the HeroService request.
You might think to use the RxJS map operator.
But the HeroService returns an Observable<Hero>.
So you flatten the Observable with the switchMap operator instead.
The switchMap operator also cancels previous in-flight requests. If the user re-navigates to this route
with a new id while the HeroService is still retrieving the old id, switchMap discards that old request and returns the hero for the new id.
The observable Subscription will be handled by the AsyncPipe and the component's hero property will be (re)set with the retrieved hero.
The ParamMap API is inspired by the URLSearchParams interface. It provides methods
to handle parameter access for both route parameters (paramMap) and query parameters (queryParamMap).
Member
Description
has(name)
Returns true if the parameter name is in the map of parameters.
get(name)
Returns the parameter name value (a string) if present, or null if the parameter name is not in the map. Returns the first element if the parameter value is actually an array of values.
getAll(name)
Returns a string array of the parameter name value if found, or an empty array if the parameter name value is not in the map. Use getAll when a single parameter could have multiple values.
In this example, you retrieve the route parameter map from an Observable.
That implies that the route parameter map can change during the lifetime of this component.
They might. By default, the router re-uses a component instance when it re-navigates to the same component type
without visiting a different component first. The route parameters could change each time.
Suppose a parent component navigation bar had "forward" and "back" buttons
that scrolled through the list of heroes.
Each click navigated imperatively to the HeroDetailComponent with the next or previous id.
You don't want the router to remove the current HeroDetailComponent instance from the DOM only to re-create it for the next id.
That could be visibly jarring.
Better to simply re-use the same component instance and update the parameter.
Unfortunately, ngOnInit is only called once per component instantiation.
You need a way to detect when the route parameters change from within the same instance.
The observable paramMap property handles that beautifully.
When subscribing to an observable in a component, you almost always arrange to unsubscribe when the component is destroyed.
There are a few exceptional observables where this is not necessary.
The ActivatedRoute observables are among the exceptions.
The ActivatedRoute and its observables are insulated from the Router itself.
The Router destroys a routed component when it is no longer needed and the injected ActivatedRoute dies with it.
Feel free to unsubscribe anyway. It is harmless and never a bad practice.
This application won't re-use the HeroDetailComponent.
The user always returns to the hero list to select another hero to view.
There's no way to navigate from one hero detail to another hero detail
without visiting the list component in between.
Therefore, the router creates a new HeroDetailComponent instance every time.
When you know for certain that a HeroDetailComponent instance will never, never, ever
be re-used, you can simplify the code with the snapshot.
The route.snapshot provides the initial value of the route parameter map.
You can access the parameters directly without subscribing or adding observable operators.
It's much simpler to write and read:
ngOnInit() {
let id = this.route.snapshot.paramMap.get('id');
this.hero$ = this.service.getHero(id);
}
ngOnInit(){let id =this.route.snapshot.paramMap.get('id');this.hero$ =this.service.getHero(id);}
Remember: you only get the initial value of the parameter map with this technique.
Stick with the observable paramMap approach if there's even a chance that the router
could re-use the component.
This sample stays with the observable paramMap strategy just in case.
The HeroDetailComponent has a "Back" button wired to its gotoHeroes method that navigates imperatively
back to the HeroListComponent.
The router navigate method takes the same one-item link parameters array
that you can bind to a [routerLink] directive.
It holds the path to the HeroListComponent:
Use route parameters to specify a required parameter value within the route URL
as you do when navigating to the HeroDetailComponent in order to view the hero with id 15:
localhost:4200/hero/15
localhost:4200/hero/15
You can also add optional information to a route request.
For example, when returning to the hero-detail.component.ts list from the hero detail view,
it would be nice if the viewed hero was preselected in the list.
You'll implement this feature in a moment by including the viewed hero's id
in the URL as an optional parameter when returning from the HeroDetailComponent.
Optional information takes other forms. Search criteria are often loosely structured, e.g., name='wind*'.
Multiple values are common—after='12/31/2015' & before='1/1/2017'—in no
particular order—before='1/1/2017' & after='12/31/2015'— in a
variety of formats—during='currentYear'.
These kinds of parameters don't fit easily in a URL path. Even if you could define a suitable URL token scheme,
doing so greatly complicates the pattern matching required to translate an incoming URL to a named route.
Optional parameters are the ideal vehicle for conveying arbitrarily complex information during navigation.
Optional parameters aren't involved in pattern matching and afford flexibility of expression.
The router supports navigation with optional parameters as well as required route parameters.
Define optional parameters in a separate object after you define the required route parameters.
In general, prefer a required route parameter when
the value is mandatory (for example, if necessary to distinguish one route path from another);
prefer an optional parameter when the value is optional, complex, and/or multivariate.
When navigating to the HeroDetailComponent you specified the requiredid of the hero-to-edit in the
route parameter and made it the second item of the link parameters array.
The router embedded the id value in the navigation URL because you had defined it
as a route parameter with an :id placeholder token in the route path:
When the user clicks the back button, the HeroDetailComponent constructs another link parameters array
which it uses to navigate back to the HeroListComponent.
This array lacks a route parameter because you had no reason to send information to the HeroListComponent.
Now you have a reason. You'd like to send the id of the current hero with the navigation request so that the
HeroListComponent can highlight that hero in its list.
This is a nice-to-have feature; the list will display perfectly well without it.
Send the id with an object that contains an optionalid parameter.
For demonstration purposes, there's an extra junk parameter (foo) in the object that the HeroListComponent should ignore.
Here's the revised navigation statement:
gotoHeroes(hero: Hero) {
let heroId = hero ? hero.id : null;
// Pass along the hero id if available
// so that the HeroList component can select that hero.
// Include a junk 'foo' property for fun.
this.router.navigate(['/heroes', { id: heroId, foo: 'foo' }]);
}
src/app/heroes/hero-detail/hero-detail.component.ts (go to heroes)
gotoHeroes(hero:Hero){let heroId = hero ? hero.id :null;// Pass along the hero id if available// so that the HeroList component can select that hero.// Include a junk 'foo' property for fun.this.router.navigate(['/heroes',{ id: heroId, foo:'foo'}]);}
The application still works. Clicking "back" returns to the hero list view.
Look at the browser address bar.
It should look something like this, depending on where you run it:
localhost:4200/heroes;id=15;foo=foo
localhost:4200/heroes;id=15;foo=foo
The id value appears in the URL as (;id=15;foo=foo), not in the URL path.
The path for the "Heroes" route doesn't have an :id token.
The optional route parameters are not separated by "?" and "&" as they would be in the URL query string.
They are separated by semicolons ";"
This is matrix URL notation—something you may not have seen before.
Matrix URL notation is an idea first introduced
in a 1996 proposal by the founder of the web, Tim Berners-Lee.
Although matrix notation never made it into the HTML standard, it is legal and
it became popular among browser routing systems as a way to isolate parameters
belonging to parent and child routes. The Router is such a system and provides
support for the matrix notation across browsers.
The syntax may seem strange to you but users are unlikely to notice or care
as long as the URL can be emailed and pasted into a browser address bar
as this one can.
Route parameters in the ActivatedRoute servicelink
The list of heroes is unchanged. No hero row is highlighted.
The live example / download exampledoes highlight the selected
row because it demonstrates the final state of the application which includes the steps you're about to cover.
At the moment this guide is describing the state of affairs prior to those steps.
The HeroListComponent isn't expecting any parameters at all and wouldn't know what to do with them.
You can change that.
Previously, when navigating from the HeroListComponent to the HeroDetailComponent,
you subscribed to the route parameter map Observable and made it available to the HeroDetailComponent
in the ActivatedRoute service.
You injected that service in the constructor of the HeroDetailComponent.
This time you'll be navigating in the opposite direction, from the HeroDetailComponent to the HeroListComponent.
First you extend the router import statement to include the ActivatedRoute service symbol:
Then you inject the ActivatedRoute in the HeroListComponent constructor.
export class HeroListComponent implements OnInit {
heroes$: Observable<Hero[]>;
selectedId: number;
constructor(
private service: HeroService,
private route: ActivatedRoute
) {}
ngOnInit() {
this.heroes$ = this.route.paramMap.pipe(
switchMap(params => {
// (+) before `params.get()` turns the string into a number
this.selectedId = +params.get('id');
return this.service.getHeroes();
})
);
}
}
src/app/heroes/hero-list/hero-list.component.ts (constructor and ngOnInit)
exportclassHeroListComponentimplementsOnInit{
heroes$:Observable<Hero[]>;
selectedId: number;constructor(private service:HeroService,private route:ActivatedRoute){}
ngOnInit(){this.heroes$ =this.route.paramMap.pipe(
switchMap(params=>{// (+) before `params.get()` turns the string into a numberthis.selectedId =+params.get('id');returnthis.service.getHeroes();}));}}
The ActivatedRoute.paramMap property is an Observable map of route parameters. The paramMap emits a new map of values that includes id
when the user navigates to the component. In ngOnInit you subscribe to those values, set the selectedId, and get the heroes.
Update the template with a class binding.
The binding adds the selected CSS class when the comparison returns true and removes it when false.
Look for it within the repeated <li> tag as shown here:
Next, add a data object to the routes for HeroListComponent and HeroDetailComponent. Transitions are based on states and you'll use the animation data from the route to provide a named animation state for the transitions.
Imports the animation symbols that build the animation triggers, control state, and manage transitions between states.
Exports a constant named slideInAnimation set to an animation trigger named routeAnimation;
Defines one transition when switching back and forth from the heroes and hero routes to ease the component in from the left of the screen as it enters the application view (:enter), the other to animate the component to the right as it leaves the application view (:leave).
You could also create more transitions for other routes. This trigger is sufficient for the current milestone.
Back in the AppComponent, import the RouterOutlet token from the @angular/router package and the slideInDownAnimation from
'./animations.ts.
Add an animations array to the @Component metadata's that contains the slideInDownAnimation.
In order to use the routable animations, you'll need to wrap the RouterOutlet inside an element. You'll
use the @routeAnimation trigger and bind it to the element.
For the @routeAnimation transitions to key off states, you'll need to provide it with the data from the ActivatedRoute. The RouterOutlet is exposed as an outlet template variable, so you bind a reference to the router outlet. A variable of routerOutlet is an ideal choice.
The @routeAnimation property is bound to the getAnimationData with the provided routerOutlet reference, so you'll need to define that function in the AppComponent. The getAnimationData function returns the animation property from the data provided through the ActivatedRoute. The animation property matches the transition names you used in the slideDownAnimation defined in animations.ts.
When switching between the two routes, the HeroDetailComponent and HeroListComponent will ease in from the left when routed to and will slide to the right when navigating away.
It's time to add real features to the app's current placeholder crisis center.
Begin by imitating the heroes feature:
Create a crisis-center subfolder in the src/app folder.
Copy the files and folders from app/heroes into the new crisis-center folder.
In the new files, change every mention of "hero" to "crisis", and "heroes" to "crises".
Rename the NgModule files to crisis-center.module.ts and crisis-center-routing.module.ts.
You'll use mock crises instead of mock heroes:
import { Crisis } from './crisis';
export const CRISES: Crisis[] = [
{ id: 1, name: 'Dragon Burning Cities' },
{ id: 2, name: 'Sky Rains Great White Sharks' },
{ id: 3, name: 'Giant Asteroid Heading For Earth' },
{ id: 4, name: 'Procrastinators Meeting Delayed Again' },
]
src/app/crisis-center/mock-crises.ts
import{Crisis}from'./crisis';exportconst CRISES:Crisis[]=[{ id:1, name:'Dragon Burning Cities'},{ id:2, name:'Sky Rains Great White Sharks'},{ id:3, name:'Giant Asteroid Heading For Earth'},{ id:4, name:'Procrastinators Meeting Delayed Again'},]
The resulting crisis center is a foundation for introducing a new concept—child routing.
You can leave Heroes in its current state as a contrast with the Crisis Center
and decide later if the differences are worthwhile.
In keeping with the
Separation of Concerns principle,
changes to the Crisis Center won't affect the AppModule or
any other feature's component.
The CrisisCenterComponent has the following in common with the AppComponent:
It is the root of the crisis center area,
just as AppComponent is the root of the entire application.
It is a shell for the crisis management feature area,
just as the AppComponent is a shell to manage the high-level workflow.
Like most shells, the CrisisCenterComponent class is very simple, simpler even than AppComponent:
it has no business logic, and its template has no links, just a title and
<router-outlet> for the crisis center child component.
Update the crisis-center-routing.module.ts you renamed after copying it from heroes-routing.module.ts file.
This time, you define child routeswithin the parent crisis-center route.
Notice that the parent crisis-center route has a children property
with a single route containing the CrisisListComponent. The CrisisListComponent route
also has a children array with two routes.
These two routes navigate to the crisis center child components,
CrisisCenterHomeComponent and CrisisDetailComponent, respectively.
There are important differences in the way the router treats these child routes.
The router displays the components of these routes in the RouterOutlet
of the CrisisCenterComponent, not in the RouterOutlet of the AppComponent shell.
The CrisisListComponent contains the crisis list and a RouterOutlet to
display the Crisis Center Home and Crisis Detail route components.
The Crisis Detail route is a child of the Crisis List. The router reuses components
by default, so the Crisis Detail component will be re-used as you select different crises.
In contrast, back in the Hero Detail route, the component was recreated each time you selected a different hero.
At the top level, paths that begin with / refer to the root of the application.
But child routes extend the path of the parent route.
With each step down the route tree,
you add a slash followed by the route path, unless the path is empty.
Apply that logic to navigation within the crisis center for which the parent path is /crisis-center.
To navigate to the CrisisCenterHomeComponent, the full URL is /crisis-center (/crisis-center + '' + '').
To navigate to the CrisisDetailComponent for a crisis with id=2, the full URL is
/crisis-center/2 (/crisis-center + '' + '/2').
The absolute URL for the latter example, including the localhost origin, is
localhost:4200/crisis-center/2
localhost:4200/crisis-center/2
Here's the complete crisis-center-routing.module.ts file with its imports.
Remove the initial crisis center route from the app-routing.module.ts.
The feature routes are now provided by the HeroesModule and the CrisisCenter modules.
The app-routing.module.ts file retains the top-level application routes such as the default and wildcard routes.
While building out the crisis center feature, you navigated to the
crisis detail route using an absolute path that begins with a slash.
The router matches such absolute paths to routes starting from the top of the route configuration.
You could continue to use absolute paths like this to navigate inside the Crisis Center
feature, but that pins the links to the parent routing structure.
If you changed the parent /crisis-center path, you would have to change the link parameters array.
You can free the links from this dependency by defining paths that are relative to the current URL segment.
Navigation within the feature area remains intact even if you change the parent route path to the feature.
Here's an example:
The router supports directory-like syntax in a link parameters list to help guide route name lookup:
./ or no leading slash is relative to the current level.
../ to go up one level in the route path.
You can combine relative navigation syntax with an ancestor path.
If you must navigate to a sibling route, you could use the ../<sibling> convention to go up
one level, then over and down the sibling route path.
To navigate a relative path with the Router.navigate method, you must supply the ActivatedRoute
to give the router knowledge of where you are in the current route tree.
After the link parameters array, add an object with a relativeTo property set to the ActivatedRoute.
The router then calculates the target URL based on the active route's location.
Always specify the complete absolute path when calling router's navigateByUrl method.
You've already injected the ActivatedRoute that you need to compose the relative navigation path.
When using a RouterLink to navigate instead of the Router service, you'd use the same
link parameters array, but you wouldn't provide the object with the relativeTo property.
The ActivatedRoute is implicit in a RouterLink directive.
Update the gotoCrises method of the CrisisDetailComponent to navigate back to the Crisis Center list using relative path navigation.
// Relative navigation back to the crises
this.router.navigate(['../', { id: crisisId, foo: 'foo' }], { relativeTo: this.route });
// Relative navigation back to the crisesthis.router.navigate(['../',{ id: crisisId, foo:'foo'}],{relativeTo:this.route });
Notice that the path goes up a level using the ../ syntax.
If the current crisis id is 3, the resulting path back to the crisis list is /crisis-center/;id=3;foo=foo.
You decide to give users a way to contact the crisis center.
When a user clicks a "Contact" button, you want to display a message in a popup view.
The popup should stay open, even when switching between pages in the application, until the user closes it
by sending the message or canceling.
Clearly you can't put the popup in the same outlet as the other pages.
Until now, you've defined a single outlet and you've nested child routes
under that outlet to group routes together.
The router only supports one primary unnamed outlet per template.
A template can also have any number of named outlets.
Each named outlet has its own set of routes with their own components.
Multiple outlets can be displaying different content, determined by different routes, all at the same time.
Add an outlet named "popup" in the AppComponent, directly below the unnamed outlet.
The path and component properties should be familiar.
There's a new property, outlet, set to 'popup'.
This route now targets the popup outlet and the ComposeMessageComponent will display there.
The user needs a way to open the popup.
Open the AppComponent and add a "Contact" link.
Although the compose route is pinned to the "popup" outlet, that's not sufficient for wiring the route to a RouterLink directive.
You have to specify the named outlet in a link parameters array and bind it to the RouterLink with a property binding.
The link parameters array contains an object with a single outlets property whose value
is another object keyed by one (or more) outlet names.
In this case there is only the "popup" outlet property and its value is another link parameters array that specifies the compose route.
You are in effect saying, when the user clicks this link, display the component associated with the compose route in the popup outlet.
This outlets object within an outer object was completely unnecessary
when there was only one route and one unnamed outlet to think about.
The router assumed that your route specification targeted the unnamed primary outlet
and created these objects for you.
Routing to a named outlet has revealed a previously hidden router truth:
you can target multiple outlets with multiple routes in the same RouterLink directive.
You're not actually doing that here.
But to target a named outlet, you must use the richer, more verbose syntax.
Secondary route navigation: merging routes during navigationlink
Navigate to the Crisis Center and click "Contact".
you should see something like the following URL in the browser address bar.
The primary navigation part has changed; the secondary route is the same.
The router is keeping track of two separate branches in a navigation tree and generating a representation of that tree in the URL.
You can add many more outlets and routes, at the top level and in nested levels, creating a navigation tree with many branches.
The router will generate the URL to go with it.
You can tell the router to navigate an entire tree at once by filling out the outlets object mentioned above.
Then pass that object inside a link parameters array to the router.navigate method.
Experiment with these possibilities at your leisure.
As you've learned, a component in an outlet persists until you navigate away to a new component.
Secondary outlets are no different in this regard.
Each secondary outlet has its own navigation, independent of the navigation driving the primary outlet.
Changing a current route that displays in the primary outlet has no effect on the popup outlet.
That's why the popup stays visible as you navigate among the crises and heroes.
Clicking the "send" or "cancel" buttons does clear the popup view.
To see how, look at the closePopup() method again:
closePopup() {
// Providing a `null` value to the named outlet
// clears the contents of the named outlet
this.router.navigate([{ outlets: { popup: null }}]);
}
closePopup(){// Providing a `null` value to the named outlet// clears the contents of the named outletthis.router.navigate([{ outlets:{ popup:null}}]);}
Like the array bound to the ContactRouterLink in the AppComponent,
this one includes an object with an outlets property.
The outlets property value is another object with outlet names for keys.
The only named outlet is 'popup'.
This time, the value of 'popup' is null. That's not a route, but it is a legitimate value.
Setting the popup RouterOutlet to null clears the outlet and removes
the secondary popup route from the current URL.
At the moment, any user can navigate anywhere in the application anytime.
That's not always the right thing to do.
Perhaps the user is not authorized to navigate to the target component.
Maybe the user must login (authenticate) first.
Maybe you should fetch some data before you display the target component.
You might want to save pending changes before leaving a component.
You might ask the user if it's OK to discard pending changes rather than save them.
You add guards to the route configuration to handle these scenarios.
A guard's return value controls the router's behavior:
If it returns true, the navigation process continues.
If it returns false, the navigation process stops and the user stays put.
Note: The guard can also tell the router to navigate elsewhere, effectively canceling the current navigation.
The guard might return its boolean answer synchronously.
But in many cases, the guard can't produce an answer synchronously.
The guard could ask the user a question, save changes to the server, or fetch fresh data.
These are all asynchronous operations.
Accordingly, a routing guard can return an Observable<boolean> or a Promise<boolean> and the
router will wait for the observable to resolve to true or false.
Note: The observable provided to the Router must also complete. If the observable does not complete, the navigation will not continue.
CanDeactivate to mediate navigation away from the current route.
Resolve to perform route data retrieval before route activation.
CanLoad to mediate navigation to a feature module loaded asynchronously.
You can have multiple guards at every level of a routing hierarchy.
The router checks the CanDeactivate and CanActivateChild guards first, from the deepest child route to the top.
Then it checks the CanActivate guards from the top down to the deepest child route. If the feature module
is loaded asynchronously, the CanLoad guard is checked before the module is loaded.
If any guard returns false, pending guards that have not completed will be canceled,
and the entire navigation is canceled.
There are several examples over the next few sections.
Applications often restrict access to a feature area based on who the user is.
You could permit access only to authenticated users or to users with a specific role.
You might block or limit access until the user's account is activated.
The CanActivate guard is the tool to manage these navigation business rules.
In this next section, you'll extend the crisis center with some new administrative features.
Those features aren't defined yet.
But you can start by adding a new feature module named AdminModule.
Generate an admin folder with a feature module file and a routing configuration file.
ng generate module admin --routing
ng generate module admin --routing
Next, generate the supporting components.
ng generate component admin/admin-dashboard
ng generate component admin/admin-dashboard
ng generate component admin/admin
ng generate component admin/admin
ng generate component admin/manage-crises
ng generate component admin/manage-crises
ng generate component admin/manage-heroes
ng generate component admin/manage-heroes
The admin feature file structure looks like this:
src/app/admin
admin
admin.component.css
admin.component.html
admin.component.ts
admin-dashboard
admin-dashboard.component.css
admin-dashboard.component.html
admin-dashboard.component.ts
manage-crises
manage-crises.component.css
manage-crises.component.html
manage-crises.component.ts
manage-heroes
manage-heroes.component.css
manage-heroes.component.html
manage-heroes.component.ts
admin.module.ts
admin-routing.module.ts
The admin feature module contains the AdminComponent used for routing within the
feature module, a dashboard route and two unfinished components to manage crises and heroes.
<h3>ADMIN</h3>
<nav>
<arouterLink="./" routerLinkActive="active"
[routerLinkActiveOptions]="{ exact: true }">Dashboard</a>
<arouterLink="./crises" routerLinkActive="active">Manage Crises</a>
<arouterLink="./heroes" routerLinkActive="active">Manage Heroes</a>
</nav>
<router-outlet></router-outlet>
<p>Dashboard</p>
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { AdminComponent } from './admin/admin.component';
import { AdminDashboardComponent } from './admin-dashboard/admin-dashboard.component';
import { ManageCrisesComponent } from './manage-crises/manage-crises.component';
import { ManageHeroesComponent } from './manage-heroes/manage-heroes.component';
import { AdminRoutingModule } from './admin-routing.module';
@NgModule({
imports: [
CommonModule,
AdminRoutingModule
],
declarations: [
AdminComponent,
AdminDashboardComponent,
ManageCrisesComponent,
ManageHeroesComponent
]
})
export class AdminModule {}
<p>Manage your crises here</p>
<p>Manage your heroes here</p>
Although the admin dashboard RouterLink only contains a relative slash without an additional URL segment, it
is considered a match to any route within the admin feature area. You only want the Dashboard link to be active when the user visits that route. Adding an additional binding to the Dashboard routerLink,[routerLinkActiveOptions]="{ exact: true }", marks the ./ link as active when the user navigates to the /admin URL and not when navigating to any of the child routes.
Component-less route: grouping routes without a componentlink
Looking at the child route under the AdminComponent, there is a path and a children
property but it's not using a component.
You haven't made a mistake in the configuration.
You've defined a component-less route.
The goal is to group the Crisis Center management routes under the admin path.
You don't need a component to do it.
A component-less route makes it easier to guard child routes.
Next, import the AdminModule into app.module.ts and add it to the imports array
to register the admin routes.
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { FormsModule } from '@angular/forms';
import { AppComponent } from './app.component';
import { PageNotFoundComponent } from './page-not-found/page-not-found.component';
import { ComposeMessageComponent } from './compose-message/compose-message.component';
import { AppRoutingModule } from './app-routing.module';
import { HeroesModule } from './heroes/heroes.module';
import { CrisisCenterModule } from './crisis-center/crisis-center.module';
import { AdminModule } from './admin/admin.module';
@NgModule({
imports: [
CommonModule,
FormsModule,
HeroesModule,
CrisisCenterModule,
AdminModule,
AppRoutingModule
],
declarations: [
AppComponent,
ComposeMessageComponent,
PageNotFoundComponent
],
bootstrap: [ AppComponent ]
})
export class AppModule { }
Currently every route within the Crisis Center is open to everyone.
The new admin feature should be accessible only to authenticated users.
You could hide the link until the user logs in. But that's tricky and difficult to maintain.
Instead you'll write a canActivate() guard method to redirect anonymous users to the
login page when they try to enter the admin area.
This is a general purpose guard—you can imagine other features
that require authenticated users—so you generate an
AuthGuard in the auth folder.
ng generate guard auth/auth
ng generate guard auth/auth
At the moment you're interested in seeing how guards work so the first version does nothing useful.
It simply logs to console and returns true immediately, allowing navigation to proceed:
Make the AuthGuard at least pretend to authenticate.
The AuthGuard should call an application service that can login a user and retain information about the current user. Generate a new AuthService in the admin folder:
ng generate service admin/auth
ng generate service admin/auth
Update the AuthService to log in the user:
import { Injectable } from '@angular/core';
import { Observable, of } from 'rxjs';
import { tap, delay } from 'rxjs/operators';
@Injectable({
providedIn: 'root',
})
export class AuthService {
isLoggedIn = false;
// store the URL so we can redirect after logging in
redirectUrl: string;
login(): Observable<boolean> {
return of(true).pipe(
delay(1000),
tap(val => this.isLoggedIn = true)
);
}
logout(): void {
this.isLoggedIn = false;
}
}
src/app/auth/auth.service.ts (excerpt)
import{Injectable}from'@angular/core';import{Observable, of }from'rxjs';import{ tap, delay }from'rxjs/operators';@Injectable({providedIn:'root',})exportclassAuthService{
isLoggedIn =false;// store the URL so we can redirect after logging in
redirectUrl:string;
login():Observable<boolean>{return of(true).pipe(
delay(1000),
tap(val =>this.isLoggedIn =true));}
logout():void{this.isLoggedIn =false;}}
Although it doesn't actually log in, it has what you need for this discussion.
It has an isLoggedIn flag to tell you whether the user is authenticated.
Its login method simulates an API call to an external service by returning an
observable that resolves successfully after a short pause.
The redirectUrl property will store the attempted URL so you can navigate to it after authenticating.
Revise the AuthGuard to call it.
import { Injectable } from '@angular/core';
import { CanActivate, ActivatedRouteSnapshot, RouterStateSnapshot, Router } from '@angular/router';
import { AuthService } from './auth.service';
@Injectable({
providedIn: 'root',
})
export class AuthGuard implements CanActivate {
constructor(private authService: AuthService, private router: Router) {}
canActivate(
next: ActivatedRouteSnapshot,
state: RouterStateSnapshot): boolean {
let url: string = state.url;
return this.checkLogin(url);
}
checkLogin(url: string): boolean {
if (this.authService.isLoggedIn) { return true; }
// Store the attempted URL for redirecting
this.authService.redirectUrl = url;
// Navigate to the login page with extras
this.router.navigate(['/login']);
return false;
}
}
src/app/auth/auth.guard.ts (v2)
import{Injectable}from'@angular/core';import{CanActivate,ActivatedRouteSnapshot,RouterStateSnapshot,Router}from'@angular/router';import{AuthService}from'./auth.service';@Injectable({providedIn:'root',})exportclassAuthGuardimplementsCanActivate{constructor(private authService:AuthService,private router:Router){}canActivate(next:ActivatedRouteSnapshot,state:RouterStateSnapshot):boolean{let url:string= state.url;returnthis.checkLogin(url);}
checkLogin(url:string):boolean{if(this.authService.isLoggedIn){returntrue;}// Store the attempted URL for redirectingthis.authService.redirectUrl = url;// Navigate to the login page with extrasthis.router.navigate(['/login']);returnfalse;}}
Notice that you inject the AuthService and the Router in the constructor.
You haven't provided the AuthService yet but it's good to know that you can inject helpful services into routing guards.
This guard returns a synchronous boolean result.
If the user is logged in, it returns true and the navigation continues.
If the user is not logged in, you store the attempted URL the user came from using the RouterStateSnapshot.url and
tell the router to navigate to a login page—a page you haven't created yet.
This secondary navigation automatically cancels the current navigation; checkLogin() returns
false just to be clear about that.
You need a LoginComponent for the user to log in to the app. After logging in, you'll redirect
to the stored URL if available, or use the default URL.
There is nothing new about this component or the way you wire it into the router configuration.
ng generate component auth/login
ng generate component auth/login
Register a /login route in the auth/auth-routing.module.ts. In app.module.ts, import and add the AuthModule to the AppModule imports.
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule } from '@angular/forms';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
import { AppComponent } from './app.component';
import { PageNotFoundComponent } from './page-not-found/page-not-found.component';
import { ComposeMessageComponent } from './compose-message/compose-message.component';
import { AppRoutingModule } from './app-routing.module';
import { HeroesModule } from './heroes/heroes.module';
import { AuthModule } from './auth/auth.module';
@NgModule({
imports: [
BrowserModule,
BrowserAnimationsModule,
FormsModule,
HeroesModule,
AuthModule,
AppRoutingModule,
],
declarations: [
AppComponent,
ComposeMessageComponent,
PageNotFoundComponent
],
bootstrap: [ AppComponent ]
})
export class AppModule {
}
<h2>LOGIN</h2>
<p>{{message}}</p>
<p>
<button (click)="login()" *ngIf="!authService.isLoggedIn">Login</button>
<button (click)="logout()" *ngIf="authService.isLoggedIn">Logout</button>
</p>
import { Component } from '@angular/core';
import { Router } from '@angular/router';
import { AuthService } from '../auth.service';
@Component({
selector: 'app-login',
templateUrl: './login.component.html',
styleUrls: ['./login.component.css']
})
export class LoginComponent {
message: string;
constructor(public authService: AuthService, public router: Router) {
this.setMessage();
}
setMessage() {
this.message = 'Logged ' + (this.authService.isLoggedIn ? 'in' : 'out');
}
login() {
this.message = 'Trying to log in ...';
this.authService.login().subscribe(() => {
this.setMessage();
if (this.authService.isLoggedIn) {
// Get the redirect URL from our auth service
// If no redirect has been set, use the default
let redirect = this.authService.redirectUrl ? this.authService.redirectUrl : '/crisis-center/admin';
// Redirect the user
this.router.navigate([redirect]);
}
});
}
logout() {
this.authService.logout();
this.setMessage();
}
}
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { FormsModule } from '@angular/forms';
import { LoginComponent } from './login/login.component';
import { AuthRoutingModule } from './auth-routing.module';
@NgModule({
imports: [
CommonModule,
FormsModule,
AuthRoutingModule
],
declarations: [
LoginComponent
]
})
export class AuthModule {}
You can also protect child routes with the CanActivateChild guard.
The CanActivateChild guard is similar to the CanActivate guard.
The key difference is that it runs before any child route is activated.
You protected the admin feature module from unauthorized access.
You should also protect child routes within the feature module.
Extend the AuthGuard to protect when navigating between the admin routes.
Open auth.guard.ts and add the CanActivateChild interface to the imported tokens from the router package.
Add the same AuthGuard to the component-less admin route to protect all other child routes at one time
instead of adding the AuthGuard to each route individually.
Back in the "Heroes" workflow, the app accepts every change to a hero immediately without hesitation or validation.
In the real world, you might have to accumulate the users changes.
You might have to validate across fields.
You might have to validate on the server.
You might have to hold changes in a pending state until the user confirms them as a group or
cancels and reverts all changes.
What do you do about unapproved, unsaved changes when the user navigates away?
You can't just leave and risk losing the user's changes; that would be a terrible experience.
It's better to pause and let the user decide what to do.
If the user cancels, you'll stay put and allow more changes.
If the user approves, the app can save.
You still might delay navigation until the save succeeds.
If you let the user move to the next screen immediately and
the save were to fail (perhaps the data are ruled invalid), you would lose the context of the error.
You can't block while waiting for the server—that's not possible in a browser.
You need to stop the navigation while you wait, asynchronously, for the server
to return with its answer.
The sample application doesn't talk to a server.
Fortunately, you have another way to demonstrate an asynchronous router hook.
Users update crisis information in the CrisisDetailComponent.
Unlike the HeroDetailComponent, the user changes do not update the crisis entity immediately.
Instead, the app updates the entity when the user presses the Save button and
discards the changes when the user presses the Cancel button.
Both buttons navigate back to the crisis list after save or cancel.
What if the user tries to navigate away without saving or canceling?
The user could push the browser back button or click the heroes link.
Both actions trigger a navigation.
Should the app save or cancel automatically?
This demo does neither. Instead, it asks the user to make that choice explicitly
in a confirmation dialog box that waits asynchronously for the user's
answer.
You could wait for the user's answer with synchronous, blocking code.
The app will be more responsive—and can do other work—by
waiting for the user's answer asynchronously. Waiting for the user asynchronously
is like waiting for the server asynchronously.
Generate a Dialog service to handle user confirmation.
ng generate service dialog
ng generate service dialog
Add a confirm() method to the DialogService to prompt the user to confirm their intent. The window.confirm is a blocking action that displays a modal dialog and waits for user interaction.
import { Injectable } from '@angular/core';
import { Observable, of } from 'rxjs';
/**
* Async modal dialog service
* DialogService makes this app easier to test by faking this service.
* TODO: better modal implementation that doesn't use window.confirm
*/
@Injectable({
providedIn: 'root',
})
export class DialogService {
/**
* Ask user to confirm an action. `message` explains the action and choices.
* Returns observable resolving to `true`=confirm or `false`=cancel
*/
confirm(message?: string): Observable<boolean> {
const confirmation = window.confirm(message || 'Is it OK?');
return of(confirmation);
};
}
const confirmation = window.confirm(message||'Is it OK?');
return of(confirmation);
};
}
It returns an Observable that resolves when the user eventually decides what to do: either
to discard changes and navigate away (true) or to preserve the pending changes and stay in the crisis editor (false).
Generate a guard that checks for the presence of a canDeactivate() method in a component—any component.
ng generate guard can-deactivate
ng generate guard can-deactivate
The CrisisDetailComponent will have this method.
But the guard doesn't have to know that.
The guard shouldn't know the details of any component's deactivation method.
It need only detect that the component has a canDeactivate() method and call it.
This approach makes the guard reusable.
Alternatively, you could make a component-specific CanDeactivate guard for the CrisisDetailComponent.
The canDeactivate() method provides you with the current
instance of the component, the current ActivatedRoute,
and RouterStateSnapshot in case you needed to access
some external information. This would be useful if you only
wanted to use this guard for this component and needed to get
the component's properties or confirm whether the router should allow navigation away from it.
import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import { CanDeactivate,
ActivatedRouteSnapshot,
RouterStateSnapshot } from '@angular/router';
import { CrisisDetailComponent } from './crisis-center/crisis-detail/crisis-detail.component';
@Injectable({
providedIn: 'root',
})
export class CanDeactivateGuard implements CanDeactivate<CrisisDetailComponent> {
canDeactivate(
component: CrisisDetailComponent,
route: ActivatedRouteSnapshot,
state: RouterStateSnapshot
): Observable<boolean> | boolean {
// Get the Crisis Center ID
console.log(route.paramMap.get('id'));
// Get the current URL
console.log(state.url);
// Allow synchronous navigation (`true`) if no crisis or the crisis is unchanged
if (!component.crisis || component.crisis.name === component.editName) {
return true;
}
// Otherwise ask the user with the dialog service and return its
// observable which resolves to true or false when the user decides
return component.dialogService.confirm('Discard changes?');
}
}
import{Injectable}from'@angular/core';import{Observable}from'rxjs';import{CanDeactivate,ActivatedRouteSnapshot,RouterStateSnapshot}from'@angular/router';import{CrisisDetailComponent}from'./crisis-center/crisis-detail/crisis-detail.component';@Injectable({providedIn:'root',})exportclassCanDeactivateGuardimplementsCanDeactivate<CrisisDetailComponent>{canDeactivate(
component:CrisisDetailComponent,
route:ActivatedRouteSnapshot,state:RouterStateSnapshot):Observable<boolean>|boolean{// Get the Crisis Center ID
console.log(route.paramMap.get('id'));// Get the current URL
console.log(state.url);// Allow synchronous navigation (`true`) if no crisis or the crisis is unchangedif(!component.crisis || component.crisis.name === component.editName){returntrue;}// Otherwise ask the user with the dialog service and return its// observable which resolves to true or false when the user decidesreturn component.dialogService.confirm('Discard changes?');}}
Looking back at the CrisisDetailComponent, it implements the confirmation workflow for unsaved changes.
canDeactivate(): Observable<boolean> | boolean {
// Allow synchronous navigation (`true`) if no crisis or the crisis is unchanged
if (!this.crisis || this.crisis.name === this.editName) {
return true;
}
// Otherwise ask the user with the dialog service and return its
// observable which resolves to true or false when the user decides
return this.dialogService.confirm('Discard changes?');
}
canDeactivate():Observable<boolean>|boolean{// Allow synchronous navigation (`true`) if no crisis or the crisis is unchangedif(!this.crisis ||this.crisis.name ===this.editName){returntrue;}// Otherwise ask the user with the dialog service and return its// observable which resolves to true or false when the user decidesreturnthis.dialogService.confirm('Discard changes?');}
Notice that the canDeactivate() method can return synchronously;
it returns true immediately if there is no crisis or there are no pending changes.
But it can also return a Promise or an Observable and the router will wait for that
to resolve to truthy (navigate) or falsy (stay put).
Add the Guard to the crisis detail route in crisis-center-routing.module.ts using the canDeactivate array property.
In the Hero Detail and Crisis Detail, the app waited until the route was activated to fetch the respective hero or crisis.
This worked well, but there's a better way.
If you were using a real world API, there might be some delay before the data to display is returned from the server.
You don't want to display a blank component while waiting for the data.
It's preferable to pre-fetch data from the server so it's ready the
moment the route is activated. This also allows you to handle errors before routing to the component.
There's no point in navigating to a crisis detail for an id that doesn't have a record.
It'd be better to send the user back to the Crisis List that shows only valid crisis centers.
In summary, you want to delay rendering the routed component until all necessary data have been fetched.
At the moment, the CrisisDetailComponent retrieves the selected crisis.
If the crisis is not found, it navigates back to the crisis list view.
The experience might be better if all of this were handled first, before the route is activated.
A CrisisDetailResolver service could retrieve a Crisis or navigate away if the Crisis does not exist
before activating the route and creating the CrisisDetailComponent.
Generate a CrisisDetailResolver service file within the Crisis Center feature area.
ng generate service crisis-center/crisis-detail-resolver
ng generate service crisis-center/crisis-detail-resolver
import { Injectable } from '@angular/core';
@Injectable({
providedIn: 'root',
})
export class CrisisDetailResolverService {
constructor() { }
}
Take the relevant parts of the crisis retrieval logic in CrisisDetailComponent.ngOnInit
and move them into the CrisisDetailResolverService.
Import the Crisis model, CrisisService, and the Router
so you can navigate elsewhere if you can't fetch the crisis.
Be explicit. Implement the Resolve interface with a type of Crisis.
Inject the CrisisService and Router and implement the resolve() method.
That method could return a Promise, an Observable, or a synchronous return value.
The CrisisService.getCrisis method returns an observable, in order to prevent the route from loading until the data is fetched.
The Router guards require an observable to complete, meaning it has emitted all
of its values. You use the take operator with an argument of 1 to ensure that the
Observable completes after retrieving the first value from the Observable returned by the
getCrisis method.
If it doesn't return a valid Crisis, return an empty Observable, canceling the previous in-flight navigation to the CrisisDetailComponent and navigate the user back to the CrisisListComponent. The update resolver service looks like this:
import { Injectable } from '@angular/core';
import {
Router, Resolve,
RouterStateSnapshot,
ActivatedRouteSnapshot
} from '@angular/router';
import { Observable, of, EMPTY } from 'rxjs';
import { mergeMap, take } from 'rxjs/operators';
import { CrisisService } from './crisis.service';
import { Crisis } from './crisis';
@Injectable({
providedIn: 'root',
})
export class CrisisDetailResolverService implements Resolve<Crisis> {
constructor(private cs: CrisisService, private router: Router) {}
resolve(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): Observable<Crisis> | Observable<never> {
let id = route.paramMap.get('id');
return this.cs.getCrisis(id).pipe(
take(1),
mergeMap(crisis => {
if (crisis) {
return of(crisis);
} else { // id not found
this.router.navigate(['/crisis-center']);
return EMPTY;
}
})
);
}
}
The CrisisDetailComponent should no longer fetch the crisis.
Update the CrisisDetailComponent to get the crisis from the ActivatedRoute.data.crisis property instead;
that's where you said it should be when you re-configured the route.
It will be there when the CrisisDetailComponent ask for it.
The router's Resolve interface is optional.
The CrisisDetailResolverService doesn't inherit from a base class.
The router looks for that method and calls it if found.
Rely on the router to call the resolver.
Don't worry about all the ways that the user could navigate away.
That's the router's job. Write this class and let the router take it from there.
The relevant Crisis Center code for this milestone follows.
<h1 class="title">Angular Router</h1>
<nav>
<arouterLink="/crisis-center" routerLinkActive="active">Crisis Center</a>
<arouterLink="/superheroes" routerLinkActive="active">Heroes</a>
<arouterLink="/admin" routerLinkActive="active">Admin</a>
<arouterLink="/login" routerLinkActive="active">Login</a>
<a [routerLink]="[{ outlets: { popup: ['compose'] } }]">Contact</a>
</nav>
<div [@routeAnimation]="getAnimationData(routerOutlet)">
<router-outlet #routerOutlet="outlet"></router-outlet>
</div>
<router-outlet name="popup"></router-outlet>
<p>Welcome to the Crisis Center</p>
<h2>CRISIS CENTER</h2>
<router-outlet></router-outlet>
import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { CrisisCenterHomeComponent } from './crisis-center-home/crisis-center-home.component';
import { CrisisListComponent } from './crisis-list/crisis-list.component';
import { CrisisCenterComponent } from './crisis-center/crisis-center.component';
import { CrisisDetailComponent } from './crisis-detail/crisis-detail.component';
import { CanDeactivateGuard } from '../can-deactivate.guard';
import { CrisisDetailResolverService } from './crisis-detail-resolver.service';
const crisisCenterRoutes: Routes = [
{
path: 'crisis-center',
component: CrisisCenterComponent,
children: [
{
path: '',
component: CrisisListComponent,
children: [
{
path: ':id',
component: CrisisDetailComponent,
canDeactivate: [CanDeactivateGuard],
resolve: {
crisis: CrisisDetailResolverService
}
},
{
path: '',
component: CrisisCenterHomeComponent
}
]
}
]
}
];
@NgModule({
imports: [
RouterModule.forChild(crisisCenterRoutes)
],
exports: [
RouterModule
]
})
export class CrisisCenterRoutingModule { }
<ul class="crises">
<li *ngFor="let crisis of crises$ | async"
[class.selected]="crisis.id === selectedId">
<a [routerLink]="[crisis.id]">
<span class="badge">{{ crisis.id }}</span>{{ crisis.name }}
</a>
</li>
</ul>
<router-outlet></router-outlet>
import { Component, OnInit } from '@angular/core';
import { ActivatedRoute } from '@angular/router';
import { CrisisService } from '../crisis.service';
import { Crisis } from '../crisis';
import { Observable } from 'rxjs';
import { switchMap } from 'rxjs/operators';
@Component({
selector: 'app-crisis-list',
templateUrl: './crisis-list.component.html',
styleUrls: ['./crisis-list.component.css']
})
export class CrisisListComponent implements OnInit {
crises$: Observable<Crisis[]>;
selectedId: number;
constructor(
private service: CrisisService,
private route: ActivatedRoute
) {}
ngOnInit() {
this.crises$ = this.route.paramMap.pipe(
switchMap(params => {
this.selectedId = +params.get('id');
return this.service.getCrises();
})
);
}
}
<div *ngIf="crisis">
<h3>"{{ editName }}"</h3>
<div>
<label>Id: </label>{{ crisis.id }}</div>
<div>
<label>Name: </label>
<input [(ngModel)]="editName" placeholder="name"/>
</div>
<p>
<button (click)="save()">Save</button>
<button (click)="cancel()">Cancel</button>
</p>
</div>
<div *ngIf="crisis">
<h3>"{{ editName }}"</h3>
<div>
<label>Id: </label>{{ crisis.id }}</div>
<div>
<label>Name: </label>
<input [(ngModel)]="editName" placeholder="name"/>
</div>
<p>
<button (click)="save()">Save</button>
<button (click)="cancel()">Cancel</button>
</p>
</div>
import { Injectable } from '@angular/core';
import {
Router, Resolve,
RouterStateSnapshot,
ActivatedRouteSnapshot
} from '@angular/router';
import { Observable, of, EMPTY } from 'rxjs';
import { mergeMap, take } from 'rxjs/operators';
import { CrisisService } from './crisis.service';
import { Crisis } from './crisis';
@Injectable({
providedIn: 'root',
})
export class CrisisDetailResolverService implements Resolve<Crisis> {
constructor(private cs: CrisisService, private router: Router) {}
resolve(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): Observable<Crisis> | Observable<never> {
let id = route.paramMap.get('id');
return this.cs.getCrisis(id).pipe(
take(1),
mergeMap(crisis => {
if (crisis) {
return of(crisis);
} else { // id not found
this.router.navigate(['/crisis-center']);
return EMPTY;
}
})
);
}
}
import { BehaviorSubject } from 'rxjs';
import { map } from 'rxjs/operators';
import { Injectable } from '@angular/core';
import { MessageService } from '../message.service';
import { Crisis } from './crisis';
import { CRISES } from './mock-crises';
@Injectable({
providedIn: 'root',
})
export class CrisisService {
static nextCrisisId = 100;
private crises$: BehaviorSubject<Crisis[]> = new BehaviorSubject<Crisis[]>(CRISES);
constructor(private messageService: MessageService) { }
getCrises() { return this.crises$; }
getCrisis(id: number | string) {
return this.getCrises().pipe(
map(crises => crises.find(crisis => crisis.id === +id))
);
}
}
import { Injectable } from '@angular/core';
import { Observable, of } from 'rxjs';
/**
* Async modal dialog service
* DialogService makes this app easier to test by faking this service.
* TODO: better modal implementation that doesn't use window.confirm
*/
@Injectable({
providedIn: 'root',
})
export class DialogService {
/**
* Ask user to confirm an action. `message` explains the action and choices.
* Returns observable resolving to `true`=confirm or `false`=cancel
*/
confirm(message?: string): Observable<boolean> {
const confirmation = window.confirm(message || 'Is it OK?');
return of(confirmation);
};
}
In the route parameters example, you only dealt with parameters specific to
the route, but what if you wanted optional parameters available to all routes?
This is where query parameters come into play.
Fragments refer to certain elements on the page
identified with an id attribute.
Update the AuthGuard to provide a session_id query that will remain after navigating to another route.
Add an anchor element so you can jump to a certain point on the page.
Add the NavigationExtras object to the router.navigate method that navigates you to the /login route.
You can also preserve query parameters and fragments across navigations without having to provide them
again when navigating. In the LoginComponent, you'll add an object as the
second argument in the router.navigate function
and provide the queryParamsHandling and preserveFragment to pass along the current query parameters
and fragment to the next route.
// Set our navigation extras object
// that passes on our global query params and fragment
let navigationExtras: NavigationExtras = {
queryParamsHandling: 'preserve',
preserveFragment: true
};
// Redirect the user
this.router.navigate([redirect], navigationExtras);
src/app/auth/login/login.component.ts (preserve)
// Set our navigation extras object// that passes on our global query params and fragmentlet navigationExtras:NavigationExtras={
queryParamsHandling:'preserve',
preserveFragment:true};// Redirect the userthis.router.navigate([redirect], navigationExtras);
The queryParamsHandling feature also provides a merge option, which will preserve and combine the current query parameters with any provided query parameters
when navigating.
As you'll be navigating to the Admin Dashboard route after logging in, you'll update it to handle the
query parameters and fragment.
import { Component, OnInit } from '@angular/core';
import { ActivatedRoute } from '@angular/router';
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';
@Component({
selector: 'app-admin-dashboard',
templateUrl: './admin-dashboard.component.html',
styleUrls: ['./admin-dashboard.component.css']
})
export class AdminDashboardComponent implements OnInit {
sessionId: Observable<string>;
token: Observable<string>;
constructor(private route: ActivatedRoute) {}
ngOnInit() {
// Capture the session ID if available
this.sessionId = this.route
.queryParamMap
.pipe(map(params => params.get('session_id') || 'None'));
// Capture the fragment if available
this.token = this.route
.fragment
.pipe(map(fragment => fragment || 'None'));
}
}
import{Component,OnInit}from'@angular/core';import{ActivatedRoute}from'@angular/router';import{Observable}from'rxjs';import{ map }from'rxjs/operators';@Component({
selector:'app-admin-dashboard',
templateUrl:'./admin-dashboard.component.html',styleUrls:['./admin-dashboard.component.css']})exportclassAdminDashboardComponentimplementsOnInit{
sessionId:Observable<string>;
token:Observable<string>;constructor(private route:ActivatedRoute){}
ngOnInit(){// Capture the session ID if availablethis.sessionId =this.route
.queryParamMap
.pipe(map(params=>params.get('session_id')||'None'));// Capture the fragment if availablethis.token =this.route
.fragment
.pipe(map(fragment => fragment ||'None'));}}
Query parameters and fragments are also available through the ActivatedRoute service.
Just like route parameters, the query parameters and fragments are provided as an Observable.
The updated Crisis Admin component feeds the Observable directly into the template using the AsyncPipe.
Now, you can click on the Admin button, which takes you to the Login
page with the provided queryParamMap and fragment. After you click the login button, notice that
you have been redirected to the Admin Dashboard page with the query parameters and fragment still intact in the address bar.
You can use these persistent bits of information for things that need to be provided across pages like
authentication tokens or session ids.
The query params and fragment can also be preserved using a RouterLink with
the queryParamsHandling and preserveFragment bindings respectively.
As you've worked through the milestones, the application has naturally gotten larger.
As you continue to build out feature areas, the overall application size will continue to grow.
At some point you'll reach a tipping point where the application takes a long time to load.
How do you combat this problem? With asynchronous routing, which loads feature modules lazily, on request.
Lazy loading has multiple benefits.
You can load feature areas only when requested by the user.
You can speed up load time for users that only visit certain areas of the application.
You can continue expanding lazy loaded feature areas without increasing the size of the initial load bundle.
You're already part of the way there.
By organizing the application into modules—AppModule,
HeroesModule, AdminModule and CrisisCenterModule—you
have natural candidates for lazy loading.
Some modules, like AppModule, must be loaded from the start.
But others can and should be lazy loaded.
The AdminModule, for example, is needed by a few authorized users, so
you should only load it when requested by the right people.
Change the adminpath in the admin-routing.module.ts from 'admin' to an empty string, '', the empty path.
The Router supports empty path routes;
use them to group routes together without adding any additional path segments to the URL.
Users will still visit /admin and the AdminComponent still serves as the Routing Component containing child routes.
Open the AppRoutingModule and add a new admin route to its appRoutes array.
Give it a loadChildren property instead of a children property, set to the address of the AdminModule.
The address is the AdminModule file location (relative to the app root),
followed by a # separator, followed by the name of the exported module class, AdminModule.
Note: When using absolute paths, the NgModule file location must begin with src/app in order to resolve correctly. For custom path mapping with absolute paths, the baseUrl and paths properties in the project tsconfig.json must be configured.
When the router navigates to this route, it uses the loadChildren string to dynamically load the AdminModule.
Then it adds the AdminModule routes to its current route configuration.
Finally, it loads the requested route to the destination admin component.
The lazy loading and re-configuration happen just once, when the route is first requested;
the module and routes are available immediately for subsequent requests.
Angular provides a built-in module loader that supports SystemJS to load modules asynchronously. If you were
using another bundling tool, such as Webpack, you would use the Webpack mechanism for asynchronously loading modules.
Take the final step and detach the admin feature set from the main application.
The root AppModule must neither load nor reference the AdminModule or its files.
In app.module.ts, remove the AdminModule import statement from the top of the file
and remove the AdminModule from the NgModule's imports array.
CanLoad Guard: guarding unauthorized loading of feature moduleslink
You're already protecting the AdminModule with a CanActivate guard that prevents unauthorized users from
accessing the admin feature area.
It redirects to the login page if the user is not authorized.
But the router is still loading the AdminModule even if the user can't visit any of its components.
Ideally, you'd only load the AdminModule if the user is logged in.
Add a CanLoad guard that only loads the AdminModule once the user is logged in and attempts to access the admin feature area.
The existing AuthGuard already has the essential logic in
its checkLogin() method to support the CanLoad guard.
Open auth.guard.ts.
Import the CanLoad interface from @angular/router.
Add it to the AuthGuard class's implements list.
Then implement canLoad() as follows:
The router sets the canLoad() method's route parameter to the intended destination URL.
The checkLogin() method redirects to that URL once the user has logged in.
Now import the AuthGuard into the AppRoutingModule and add the AuthGuard to the canLoad
array property for the admin route.
The completed admin route looks like this:
Preloading: background loading of feature areaslink
You've learned how to load modules on-demand.
You can also load modules asynchronously with preloading.
This may seem like what the app has been doing all along. Not quite.
The AppModule is loaded when the application starts; that's eager loading.
Now the AdminModule loads only when the user clicks on a link; that's lazy loading.
Preloading is something in between.
Consider the Crisis Center.
It isn't the first view that a user sees.
By default, the Heroes are the first view.
For the smallest initial payload and fastest launch time,
you should eagerly load the AppModule and the HeroesModule.
You could lazy load the Crisis Center.
But you're almost certain that the user will visit the Crisis Center within minutes of launching the app.
Ideally, the app would launch with just the AppModule and the HeroesModule loaded
and then, almost immediately, load the CrisisCenterModule in the background.
By the time the user navigates to the Crisis Center, its module will have been loaded and ready to go.
After each successful navigation, the router looks in its configuration for an unloaded module that it can preload.
Whether it preloads a module, and which modules it preloads, depends upon the preload strategy.
The Router offers two preloading strategies out of the box:
No preloading at all which is the default. Lazy loaded feature areas are still loaded on demand.
Preloading of all lazy loaded feature areas.
Out of the box, the router either never preloads, or preloads every lazy load module.
The Router also supports custom preloading strategies for
fine control over which modules to preload and when.
In this next section, you'll update the CrisisCenterModule to load lazily
by default and use the PreloadAllModules strategy
to load it (and all other lazy loaded modules) as soon as possible.
You could try this now and confirm that the CrisisCenterModule loads after you click the "Crisis Center" button.
To enable preloading of all lazy loaded modules, import the PreloadAllModules token from the Angular router package.
The second argument in the RouterModule.forRoot method takes an object for additional configuration options.
The preloadingStrategy is one of those options.
Add the PreloadAllModules token to the forRoot call:
This tells the Router preloader to immediately load all lazy loaded routes (routes with a loadChildren property).
When you visit http://localhost:4200, the /heroes route loads immediately upon launch
and the router starts loading the CrisisCenterModule right after the HeroesModule loads.
Surprisingly, the AdminModule does not preload. Something is blocking it.
The PreloadAllModules strategy does not load feature areas protected by a CanLoad guard.
This is by design.
You added a CanLoad guard to the route in the AdminModule a few steps back
to block loading of that module until the user is authorized.
That CanLoad guard takes precedence over the preload strategy.
If you want to preload a module and guard against unauthorized access,
drop the canLoad() guard method and rely on the canActivate() guard alone.
Preloading every lazy loaded modules works well in many situations,
but it isn't always the right choice, especially on mobile devices and over low bandwidth connections.
You may choose to preload only certain feature modules, based on user metrics and other business and technical factors.
You can control what and how the router preloads with a custom preloading strategy.
In this section, you'll add a custom strategy that only preloads routes whose data.preload flag is set to true.
Recall that you can add anything to the data property of a route.
Set the data.preload flag in the crisis-center route in the AppRoutingModule.
import{Injectable}from'@angular/core';import{PreloadingStrategy,Route}from'@angular/router';import{Observable, of }from'rxjs';@Injectable({providedIn:'root',})exportclassSelectivePreloadingStrategyServiceimplementsPreloadingStrategy{
preloadedModules:string[]=[];
preload(route:Route, load:()=>Observable<any>):Observable<any>{if(route.data && route.data['preload']){// add the route path to the preloaded module arraythis.preloadedModules.push(route.path);// log the route path to the console
console.log('Preloaded: '+ route.path);return load();}else{return of(null);}}}
SelectivePreloadingStrategyService implements the PreloadingStrategy, which has one method, preload.
The router calls the preload method with two arguments:
The route to consider.
A loader function that can load the routed module asynchronously.
An implementation of preload must return an Observable.
If the route should preload, it returns the observable returned by calling the loader function.
If the route should not preload, it returns an Observable of null.
In this sample, the preload method loads the route if the route's data.preload flag is truthy.
It also has a side-effect.
SelectivePreloadingStrategyService logs the path of a selected route in its public preloadedModules array.
Shortly, you'll extend the AdminDashboardComponent to inject this service and display its preloadedModules array.
But first, make a few changes to the AppRoutingModule.
Import SelectivePreloadingStrategyService into AppRoutingModule.
Replace the PreloadAllModules strategy in the call to forRoot with this SelectivePreloadingStrategyService.
Add the SelectivePreloadingStrategyService strategy to the AppRoutingModule providers array so it can be injected
elsewhere in the app.
Now edit the AdminDashboardComponent to display the log of preloaded routes.
Import the SelectivePreloadingStrategyService.
Inject it into the dashboard's constructor.
Update the template to display the strategy service's preloadedModules array.
When you're done it looks like this.
import { Component, OnInit } from '@angular/core';
import { ActivatedRoute } from '@angular/router';
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';
import { SelectivePreloadingStrategyService } from '../../selective-preloading-strategy.service';
@Component({
selector: 'app-admin-dashboard',
templateUrl: './admin-dashboard.component.html',
styleUrls: ['./admin-dashboard.component.css']
})
export class AdminDashboardComponent implements OnInit {
sessionId: Observable<string>;
token: Observable<string>;
modules: string[];
constructor(
private route: ActivatedRoute,
preloadStrategy: SelectivePreloadingStrategyService
) {
this.modules = preloadStrategy.preloadedModules;
}
ngOnInit() {
// Capture the session ID if available
this.sessionId = this.route
.queryParamMap
.pipe(map(params => params.get('session_id') || 'None'));
// Capture the fragment if available
this.token = this.route
.fragment
.pipe(map(fragment => fragment || 'None'));
}
}
import{Component,OnInit}from'@angular/core';import{ActivatedRoute}from'@angular/router';import{Observable}from'rxjs';import{ map }from'rxjs/operators';import{SelectivePreloadingStrategyService}from'../../selective-preloading-strategy.service';@Component({
selector:'app-admin-dashboard',
templateUrl:'./admin-dashboard.component.html',styleUrls:['./admin-dashboard.component.css']})exportclassAdminDashboardComponentimplementsOnInit{
sessionId:Observable<string>;
token:Observable<string>;
modules:string[];constructor(private route:ActivatedRoute,
preloadStrategy:SelectivePreloadingStrategyService){this.modules = preloadStrategy.preloadedModules;}
ngOnInit(){// Capture the session ID if availablethis.sessionId =this.route
.queryParamMap
.pipe(map(params=>params.get('session_id')||'None'));// Capture the fragment if availablethis.token =this.route
.fragment
.pipe(map(fragment => fragment ||'None'));}}
Once the application loads the initial route, the CrisisCenterModule is preloaded.
Verify this by logging in to the Admin feature area and noting that the crisis-center is listed in the Preloaded Modules.
It's also logged to the browser's console.
You've setup the routes for navigating around your application. You've used navigation imperatively and declaratively to many different routes. But like any application, requirements change over time. You've setup links and navigation to /heroes and /hero/:id from the HeroListComponent and HeroDetailComponent components. If there was a requirement that links to heroes become superheroes, you still want the previous URLs to navigate correctly. You also don't want to go and update every link in your application, so redirects makes refactoring routes trivial.
Let's take the Hero routes and migrate them to new URLs. The Router checks for redirects in your configuration before navigating, so each redirect is triggered when needed. To support this change, you'll add redirects from the old routes to the new routes in the heroes-routing.module.
You'll notice two different types of redirects. The first change is from /heroes to /superheroes without any parameters. This is a straightforward redirect, unlike the change from /hero/:id to /superhero/:id, which includes the :id route parameter. Router redirects also use powerful pattern matching, so the Router inspects the URL and replaces route parameters in the path with their appropriate destination. Previously, you navigated to a URL such as /hero/15 with a route parameter id of 15.
When using absolute redirects, the Router will use the query parameters and the fragment from the redirectTo in the route config.
When using relative redirects, the Router use the query params and the fragment from the source URL.
Before updating the app-routing.module.ts, you'll need to consider an important rule. Currently, our empty path route redirects to /heroes, which redirects to /superheroes. This won't work and is by design as the Router handles redirects once at each level of routing configuration. This prevents chaining of redirects, which can lead to endless redirect loops.
So instead, you'll update the empty path route in app-routing.module.ts to redirect to /superheroes.
RouterLinks aren't tied to route configuration, so you'll need to update the associated router links so they remain active when the new route is active. You'll update the app.component.ts template for the /heroes routerLink.
Update the goToHeroes() method in the hero-detail.component.ts to navigate back to /superheroes with the optional route parameters.
gotoHeroes(hero: Hero) {
let heroId = hero ? hero.id : null;
// Pass along the hero id if available
// so that the HeroList component can select that hero.
// Include a junk 'foo' property for fun.
this.router.navigate(['/superheroes', { id: heroId, foo: 'foo' }]);
}
gotoHeroes(hero:Hero){let heroId = hero ? hero.id :null;// Pass along the hero id if available// so that the HeroList component can select that hero.// Include a junk 'foo' property for fun.this.router.navigate(['/superheroes',{ id: heroId, foo:'foo'}]);}
With the redirects setup, all previous routes now point to their new destinations and both URLs still function as intended.
You put a lot of effort into configuring the router in several routing module files
and were careful to list them in the proper order.
Are routes actually evaluated as you planned?
How is the router really configured?
You can inspect the router's current configuration any time by injecting it and
examining its config property.
For example, update the AppModule as follows and look in the browser console window
to see the finished route configuration.
export class AppModule {
// Diagnostic only: inspect router configuration
constructor(router: Router) {
// Use a custom replacer to display function names in the route configs
const replacer = (key, value) => (typeof value === 'function') ? value.name : value;
console.log('Routes: ', JSON.stringify(router.config, replacer, 2));
}
}
src/app/app.module.ts (inspect the router config)
exportclassAppModule{// Diagnostic only: inspect router configurationconstructor(router:Router){// Use a custom replacer to display function names in the route configsconst replacer =(key,value)=>(typeofvalue==='function')?value.name :value;
console.log('Routes: ', JSON.stringify(router.config, replacer,2));}}
You've covered a lot of ground in this guide and the application is too big to reprint here.
Please visit the Router Sample in Stackblitz / download example
where you can download the final source code.
These three examples cover the need for an app with one level routing.
The moment you add a child router, such as the crisis center, you create new link array possibilities.
Recall that you specified a default child route for the crisis center so this simple RouterLink is fine.
In sum, you can write applications with one, two or more levels of routing.
The link parameters array affords the flexibility to represent any routing depth and
any legal sequence of route paths, (required) router parameters, and (optional) route parameter objects.
Appendix: LocationStrategy and browser URL styleslink
When the router navigates to a new component view, it updates the browser's location and history
with a URL for that view.
This is a strictly local URL. The browser shouldn't send this URL to the server
and should not reload the page.
Modern HTML5 browsers support
history.pushState,
a technique that changes a browser's location and history without triggering a server page request.
The router can compose a "natural" URL that is indistinguishable from
one that would otherwise require a page load.
Here's the Crisis Center URL in this "HTML5 pushState" style:
localhost:3002/crisis-center/
localhost:3002/crisis-center/
Older browsers send page requests to the server when the location URL changes
unless the change occurs after a "#" (called the "hash").
Routers can take advantage of this exception by composing in-application route
URLs with hashes. Here's a "hash URL" that routes to the Crisis Center.
localhost:3002/src/#/crisis-center/
localhost:3002/src/#/crisis-center/
The router supports both styles with two LocationStrategy providers:
The RouterModule.forRoot function sets the LocationStrategy to the PathLocationStrategy,
making it the default strategy.
You can switch to the HashLocationStrategy with an override during the bootstrapping process if you prefer it.
You must choose a strategy and you need to make the right call early in the project.
It won't be easy to change later once the application is in production
and there are lots of application URL references in the wild.
Almost all Angular projects should use the default HTML5 style.
It produces URLs that are easier for users to understand.
And it preserves the option to do server-side rendering later.
Rendering critical pages on the server is a technique that can greatly improve
perceived responsiveness when the app first loads.
An app that would otherwise take ten or more seconds to start
could be rendered on the server and delivered to the user's device
in less than a second.
This option is only available if application URLs look like normal web URLs
without hashes (#) in the middle.
Stick with the default unless you have a compelling reason to
resort to hash routes.
The router uses the browser's
history.pushState
for navigation. Thanks to pushState, you can make in-app URL paths look the way you want them to
look, e.g. localhost:4200/crisis-center. The in-app URLs can be indistinguishable from server URLs.
Modern HTML5 browsers were the first to support pushState which is why many people refer to these URLs as
"HTML5 style" URLs.
HTML5 style navigation is the router default.
In the LocationStrategy and browser URL styles Appendix,
learn why HTML5 style is preferred, how to adjust its behavior, and how to switch to the
older hash (#) style, if necessary.
You must add a
<base href> element
to the app's index.html for pushState routing to work.
The browser uses the <base href> value to prefix relative URLs when referencing
CSS files, scripts, and images.
Add the <base> element just after the <head> tag.
If the app folder is the application root, as it is for this application,
set the href value in index.htmlexactly as shown here.
Without that tag, the browser may not be able to load resources
(images, CSS, scripts) when "deep linking" into the app.
Bad things could happen when someone pastes an application link into the
browser's address bar or clicks such a link in an email.
Some developers may not be able to add the <base> element, perhaps because they don't have
access to <head> or the index.html.
Those developers may still use HTML5 URLs by taking two remedial steps:
Provide the router with an appropriate APP_BASE_HREF value.
Use root URLs for all web resources: CSS, images, scripts, and template HTML files.
You can go old-school with the HashLocationStrategy by
providing the useHash: true in an object as the second argument of the RouterModule.forRoot
in the AppModule.
