foo.ts

const vat_input: HTMLInputElement = document.querySelector(".vat_input");
const netto_input: HTMLInputElement = document.querySelector(".netto_input");
const add_inputs_button: HTMLButtonElement = document.querySelector(".add_inputs_button");
const result_value: HTMLDivElement = document.querySelector(".result_value");

const vatInputEvent$ = fromEvent(vat_input, 'change').pipe(
  pluck('target', 'value'),
  map((val) => val ? parseFloat(String(val)) : 0),
  map((val) => isFloat(val) ? parseFloat(val.toFixed(2)) : val),
  distinctUntilChanged(),
);
const nettoInputEvent$ = fromEvent(netto_input, 'change').pipe(
  pluck('target', 'value'),
  map((val) => val ? parseFloat(String(val)) : 0),
  map((val) => isFloat(val) ? parseFloat(val.toFixed(2)) : val),
  distinctUntilChanged(),
);
const foo$ = combineLatest([vatInputEvent$, nettoInputEvent$], (a,b) => {
  return {a,b}
});
const addInputsValueButton$ = fromEvent(add_inputs_button, 'click').subscribe(() => WHAT NOW?); // How to get values from foo$ here?