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

When a call returns a Promise chain the calls with

someFunction() {
  return returnsPromise()
    .then(result => doSomethingNext())
    .then(result => doSomethingAfterThat());
}

Ensure you have a return that returns the Promise of that chain so the caller of someFunc() also has a chance to time additional work to execute after doSomethingAfterThat() is completed.

When a call returns an Observable then use the complete callback

someFunction() {
  return returnsObservable()
    .subscribe(
      event => doForEachEvent(),
      error => handleError(),
      () => doSomethingNext()
          .then(result => doSomethingAfterThat());
}

doSomethingNext() is executed after the last event and doSomethingAfterThat() is again chained with then() to show how to mix observable and promise. doSomething().