Angular's "CanActivate" interface is deprecated. How to replace it?

Question

My Angular app includes a simple AuthGuard as shown below and there has never been a problem with it. Recently, I upgraded my Angular version from 15.1.4 to 15.2.0 and since then, my IDE indicates that both CanActivate and CanActivateChild are deprecated.

The official Angular documentation for CanActivate says:

Deprecated: Use plain JavaScript functions instead.

How would I need to adjust the code below to get rid of the deprecated warning?

export class AuthGuard implements CanActivate, CanActivateChild {

    constructor(private authService: AuthenticationService) {}

    canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): Observable<boolean | UrlTree> | Promise<boolean | UrlTree> | boolean | UrlTree  {
        return this.authService.checkLogin()
            .pipe(
                map(() => true),
                catchError(() => {
                    this.router.navigate(['route-to-fallback-page']);
                    return of(false);
                }
            )
        );
    }

    canActivateChild(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): Observable<boolean | UrlTree> | Promise<boolean | UrlTree> | boolean | UrlTree {
        return this.canActivate(route, state);
    }
}

Answer 1

v18 Answer:

CanActivate has been un-deprecated in v18. See this PR

I'd still recommend to migrate to CanActivateFn.

---

Pre v18 answer.

The trick is to rely on inject() for the injection of the instances you need :

export const canActivate: CanActivateFn = (
  route: ActivatedRouteSnapshot,
  state: RouterStateSnapshot
) => {
  const authService = inject(AuthenticationService);
  const router = inject(Router);

  return authService.checkLogin().pipe(
    map(() => true),
    catchError(() => {
      return router.createUrlTree(['route-to-fallback-page']);
    })
  );
};

export const canActivateChild: CanActivateChildFn = (route: ActivatedRouteSnapshot, state: RouterStateSnapshot) => canActivate(route, state);

inject() allows you to use the dependency injection when you are in an injection context. For example in a constructor or like here when passing a function to a core Angular feature.

You can also read about it on the deprecation list.

Also Since v16, Angular provides some helper functions to convert classes to functionnal guards like mapToCanActivate :

@Injectable({providedIn: 'root'})
export class AdminGuard {
  canActivate() {
    return true;
  }
}

const route: Route = {
  path: 'admin',
  canActivate: mapToCanActivate([AdminGuard]),
};

You can find the others here.