RxJS combineLatest() accepts a selector function

The RxJS function combineLatest() accepts a selector function as last parameter. This selector function receives the latest value of each observable as argument and can be used to return a new value that will be emitted.

combineLatest(
  // Array of observables
  [stream1$, stream2$, stream3$],

  // Selector function
  (val1, val2, val3) => val1 + val2 + val3 // Return value will be emitted
).subscribe();