Angular show spinner for every HTTP request with very less code changes

@jornare has a good idea in his solution. He's handling the case for multiple requests. However, the code could be written simpler, without creating new observable and storing requests in memory. The below code also uses RxJS 6 with pipeable operators:

import { Injectable } from '@angular/core';
import {
  HttpRequest,
  HttpHandler,
  HttpInterceptor,
  HttpResponse
} from '@angular/common/http';
import { finalize } from 'rxjs/operators';
import { LoadingService } from '@app/services/loading.service';
import { of } from 'rxjs';

@Injectable()
export class LoadingInterceptor implements HttpInterceptor {
  private totalRequests = 0;

  constructor(private loadingService: LoadingService) { }

  intercept(request: HttpRequest<any>, next: HttpHandler) {
    this.totalRequests++;
    this.loadingService.setLoading(true);

    return next.handle(request).pipe(
      finalize(res => {
        this.totalRequests--;
        if (this.totalRequests === 0) {
          this.loadingService.setLoading(false);
        }
      })
    );
  }
}

Add this interceptor service into your module providers:

@NgModule({
  // ...
  providers: [
    { provide: HTTP_INTERCEPTORS, useClass: LoadingInterceptor, multi: true }
  ]
})
export class AppModule { }

Here's an example of the LoadingService implementation:

@Injectable()
export class LoadingService {
  private isLoading$$ = new BehaviorSubject<boolean>(false);
  isLoading$ = this.isLoading$$.asObservable();
  
  setLoading(isLoading: boolean) {
    this.isLoading$$.next(isLoading);
  }
}

And here's how you'd use the LoadingService in a component:

@Component({
  selector: 'app-root',
  template: `
    <ng-container *ngIf="loadingService.isLoading$ | async">
      <i class="loading"></i>
    </ng-container>
    <router-outlet></router-outlet>
  `,
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class AppComponent {
  constructor(public loadingService: LoadingService) {}
}

Angular 4+ has a new HttpClient which supports HttpInterceptors. This allows you to insert code that will be run whenever you make a HTTP request.

It is important to notice that HttpRequest are not long-lived Observables, but they terminate after the response. Furthermore, if the observable is unsubscribed before the response has returned, the request is cancelled and neither of the handlers are being processed. You may therefore end up with a "hanging" loader bar, which never goes away. This typically happens if you navigate a bit fast in your application.

To get around this last issue, we need to create a new Observable to be able to attach teardown-logic.

We return this rather than the original Observable. We also need to keep track of all requests made, because we may run more than one request at a time.

We also need a service which can hold and share the state of whether we have pending requests.

@Injectable()
export class MyLoaderService {
    // A BehaviourSubject is an Observable with a default value
    public isLoading = new BehaviorSubject<boolean>(false);

    constructor() {}
}

The Interceptor uses the MyLoaderService

@Injectable()
export class MyLoaderInterceptor implements HttpInterceptor {
    private requests: HttpRequest<any>[] = [];

    constructor(private loaderService: MyLoaderService) { }

    removeRequest(req: HttpRequest<any>) {
        const i = this.requests.indexOf(req);
        this.requests.splice(i, 1);
        this.loaderService.isLoading.next(this.requests.length > 0);
    }

    intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        this.requests.push(req);
        this.loaderService.isLoading.next(true);
        return Observable.create(observer => {
          const subscription = next.handle(req)
            .subscribe(
            event => {
              if (event instanceof HttpResponse) {
                this.removeRequest(req);
                observer.next(event);
              }
            },
            err => { this.removeRequest(req); observer.error(err); },
            () => { this.removeRequest(req); observer.complete(); });
          // teardown logic in case of cancelled requests
          return () => {
            this.removeRequest(req);
            subscription.unsubscribe();
          };
        });
    }
}

Finally, in our Component, we can use the same MyLoaderService and with the async operator we do not even need to subscribe. Since the source value we want to use is from a service, it should be shared as an Observable so that it gets a rendering scope/zone where it is used. If it is just a value, it may not update your GUI as wanted.

@Component({...})
export class MyComponent {
    constructor(public myLoaderService: MyLoaderService) {}
}

And an example template using async

<div class="myLoadBar" *ngIf="myLoaderService.isLoading | async">Loading!</div>

I assume you know how to provide services and set up modules properly. You can also see a working example at Stackblitz

In Angular 5 comes the HttpClient module. You can find more information there.

With this module, come something called interceptors.

They allow you to do something for every HTTP request.

If you migrate from Http to HttpClient (and you should, Http will be deprecated), you can create an interceptor that can handle a variable in a shared service :

intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    this.sharedService.loading = true;
    return next
      .handle(req)
      .finally(() => this.sharedService.loading = false);
}

Now you just have to use this variable into your templates.

<spinner *ngIf="sharedService.loading"></spinner>

(Be sure to have an injection of your service in the components that display this spinner)

This is a basic loading dialog that can be toggled with an angular property. Just add *ngIf="loader" to the center-loader and set the property appropriately

.center-loader {
    font-size: large;
    position:absolute;
    z-index:1000;
    top: 50%;
    left: 50%;
    -ms-transform: translate(-50%, -50%);
    transform: translate(-50%, -50%);
}

@keyframes blink {50% { color: transparent }}
.loader__dot { animation: 1s blink infinite; font-size: x-large;}
.loader__dot:nth-child(2) { animation-delay: 250ms; font-size: x-large;}
.loader__dot:nth-child(3) { animation-delay: 500ms; font-size: x-large;}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.2.3/jquery.min.js"></script>
<div class="center-loader">
  <strong>Loading
  <span class="loader__dot">.</span>
  <span class="loader__dot">.</span>
  <span class="loader__dot">.</span></strong>
</div>

Initialize the loader to true for each page, and then set to false once the service finished:

Top of component:

export class MyComponent implements OnInit {
    loader:boolean = true;
//...

onInit():

 await this.myService
    .yourServiceCall()
    .then(result => {
        this.resultsSet=result);
        this.loader = false;      // <- hide the loader
      }
    .catch(error => console.log(error));

Depends upon the approach you follow to use REST SERVICES

My approach is

• Create a component and place it somewhere in the application level.

• Create a service which has counter with increment and decrements methods.

• This service should decide to show the loader(component) or not by following the below steps.

  Increase the counter each for one request from the client.

  Decrease the counter on each response success and failure