Angular2 - How to chain async service calls (http requests) in a component?

Question

I have a component which first need to call a service that POST something. Then in the same component I want to wait until the POST is done, to call another service which

Answer 1

Better use switchMap() here.

const versions$ = this._newVersionService.createNewVersion(vnr)
                 .switchMap(response => this._versionService.getAvailableVersions());

versions$.subscribe(response2 => this.versions = response2)

But the problem will be if you make another POST request before first has been resolved, the previous request will get cancelled.