Angular 2 - Chaining http requests

Source: https://stackoverflow.com/questions/42626536/angular-2-chaining-http-requests
https://stackoverflow.com/questions/49002681/send-multiple-requests-in-sequence-in-angular-5-resolver

Chaining HTTP requests can be achieved using the Observable.flatMap operator. Say we want to make three requests where each request depends on the result of previous one:

this.service.firstMethod()
    .flatMap(firstMethodResult => this.service.secondMethod(firstMethodResult))
    .flatMap(secondMethodResult => this.service.thirdMethod(secondMethodResult))
    .subscribe(thirdMethodResult => {
          console.log(thirdMethodResult);
     });

This way you can chain as much interdependent requests you want

I had a similar problem where I ended up using flatMap callback, basically from the documentation, it allows us to perform sequential tasks and return observable in the end.

You can try something like in the resolve function of the resolver,

return request1().flatMap( (response: any) => {
    return forkJoin( [ request2(), request3() ];
} );

Where request1 is the function that you want to be performed before request2 and request3 are executed. It goes without saying that, all the requests must be returning Observables.

More: https://coryrylan.com/blog/angular-multiple-http-requests-with-rxjs