@lifaon/rx-js-light/src/observable/pipes/built-in/without-notifications/others/conditional/conditional-observable.mjs

Blazing fast Observables

export function conditionalObservable(subscribe, condition) {
  return emit => {
    let running = true;
    let unsubscribe = null;
    let lastValue;
    const _unsubscribe = () => {
      if (unsubscribe !== null) {
        unsubscribe();
        unsubscribe = null;
      }
    };
    const unsubscribeOfCondition = condition(value => {
      if (value !== lastValue) {
        lastValue = value;
        _unsubscribe();
        if (value && running) {
          unsubscribe = subscribe(emit);
        }
      }
    });
    return () => {
      if (running) {
        running = false;
        unsubscribeOfCondition();
        _unsubscribe();
      }
    };
  };
}