Tutorial: Creating custom route matches

The Angular Router supports a powerful matching strategy that you can use to help users navigate your application. This matching strategy supports static routes, variable routes with parameters, wildcard routes, and so on. Also, build your own custom pattern matching for situations in which the URLs are more complicated.

In this tutorial, you'll build a custom route matcher using Angular's UrlMatcher. This matcher looks for a Twitter handle in the URL.

For a working example of the final version of this tutorial, see the live example.

Objectives

Implement Angular's UrlMatcher to create a custom route matcher.

Prerequisites

To complete this tutorial, you should have a basic understanding of the following concepts:

• JavaScript
• HTML
• CSS
• Angular CLI

If you are unfamiliar with how Angular's router works, review Using Angular routes in a single-page application.

Create a sample application

Using the Angular CLI, create a new application, angular-custom-route-match. In addition to the default Angular application framework, you will also create a profile component.

1. Create a new Angular project, angular-custom-route-match.

   ng new angular-custom-route-match

   When prompted with Would you like to add Angular routing?, select Y.

   When prompted with Which stylesheet format would you like to use?, select CSS.

   After a few moments, a new project, angular-custom-route-match, is ready.

2. From your terminal, navigate to the angular-custom-route-match directory.

3. Create a component, profile.

   ng generate component profile

4. In your code editor, locate the file, profile.component.html and replace the placeholder content with the following HTML.

   <p>
   Hello {{ username$ | async }}!
   </p>

5. In your code editor, locate the file, app.component.html and replace the placeholder content with the following HTML.

   <h2>Routing with Custom Matching</h2>
   
   Navigate to <a routerLink="/@Angular">my profile</a>
   
   <router-outlet></router-outlet>

Configure your routes for your application

With your application framework in place, you next need to add routing capabilities to the app.module.ts file. As a part of this process, you will create a custom URL matcher that looks for a Twitter handle in the URL. This handle is identified by a preceding @ symbol.

1. In your code editor, open your app.module.ts file.

2. Add an import statement for Angular's RouterModule and UrlMatcher.

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

3. In the imports array, add a RouterModule.forRoot([]) statement.

   @NgModule({
     imports:      [
       BrowserModule,
       FormsModule,
       RouterModule.forRoot([
   /* . . . */
       ])],
     declarations: [ AppComponent, ProfileComponent ],
     bootstrap:    [ AppComponent ]
   })

4. Define the custom route matcher by adding the following code to the RouterModule.forRoot() statement.

   {
     matcher: (url) => {
       if (url.length === 1 && url[0].path.match(/^@[\w]+$/gm)) {
         return {
           consumed: url,
           posParams: {
             username: new UrlSegment(url[0].path.slice(1), {})
           }
         };
       }
   
       return null;
     },
     component: ProfileComponent
   }

This custom matcher is a function that performs the following tasks:

• The matcher verifies that the array contains only one segment
• The matcher employs a regular expression to ensure that the format of the username is a match
• If there is a match, the function returns the entire URL, defining a username route parameter as a substring of the path
• If there isn't a match, the function returns null and the router continues to look for other routes that match the URL

Subscribe to the route parameters

With the custom matcher in place, you now need to subscribe to the route parameters in the profile component.

1. In your code editor, open your profile.component.ts file.

2. Add an import statement for Angular's ActivatedRoute and ParamMap.

   import { ActivatedRoute, ParamMap } from '@angular/router';

3. Add an import statement for RxJS map.

   import { map } from 'rxjs/operators';

4. Subscribe to the username route parameter.

   username$ = this.route.paramMap
     .pipe(
       map((params: ParamMap) => params.get('username'))
     );

5. Inject the ActivatedRoute into the component's constructor.

   constructor(private route: ActivatedRoute) { }

Test your custom URL matcher

With your code in place, you can now test your custom URL matcher.

1. From a terminal window, run the ng serve command.

   ng serve

2. Open a browser to http://localhost:4200.

   You should see a single web page, consisting of a sentence that reads Navigate to my profile.

3. Click the my profile hyperlink.

   A new sentence, reading Hello, Angular! appears on the page.

Next steps

Pattern matching with the Angular Router provides you with a lot of flexibility when you have dynamic URLs in your application. To learn more about the Angular Router, see the following topics:

• In-app Routing and Navigation
• Router API

This content is based on Custom Route Matching with the Angular Router, by Brandon Roberts.