function-to-observable.js

// A public observable
export const myObservable = RxJS.something(
  // ?
);

// A function I can call any time to emit `val` from `myObservable`
function secretFunction(val) {
  // ?
}

const mySubject = new RxJS.Subject();

export function getMyObservable() {
  return mySubject.asObservable();
}

export function secretFunction(val) {
  mySubject.next(val);
}

// There's nothing up there to complete the subject - there should be a 'done' :
export function imDone() {
  mySubject.complete();
}