Design, Implementation, and Performance Benefits of a New React Hook for Controlling Flow

In the article "React 新 hook 尝鲜" the author examines the design philosophy and constraints of a new React Hook named use , which can be invoked inside control flow, and presents a prototype implementation to help readers understand the concept.

The author argues that the Hook’s ambition goes beyond simple usage, suggesting a future where the Hook accepts a generic "usable" type, with the first official "usable" being React Context, allowing calls like use(Context) to replace useContext(Context) .

To illustrate how external resources can be consumed, the article walks through a useBehaviorSubject example based on RxJS’s BehaviorSubject , showing two implementations: one that forces a re‑render on every emission and an optimized version that stores the value in fiber state to avoid unnecessary renders.

function useBehaviorSubject(subject) {
  const [, setState] = useState(0);
  useEffect(() => {
    const subscription = subject.subscribe(() => {
      // force rerender
      setState(x => x + 1);
    });
    return () => subscription.unsubscribe();
  }, [subject]);
  // return the value of this subject.
  return subject.getValue();
}

In concurrent mode, using useEffect for external subscriptions can cause tearing, so the article recommends useSyncExternalStore to temporarily disable time‑slicing and update synchronously.

function useBehaviorSubject(subject) {
  return useSyncExternalStore(subject.subscribe, subject.getValue);
}

The author identifies three main challenges when React interacts with external resources: invalid renders, the need to temporarily disable concurrent mode, and a space‑for‑time trade‑off.

To address these, a new Hook use is proposed that retains the ability to be called in control flow while eliminating the three problems. The article suggests lazy subscription ("lazy subscribe") as a core idea: only subscribe when the value is actually read, thereby preventing unnecessary renders.

function useBehaviorSubject(subject) {
  const subscriptionRef = useRef(null);
  const [value, setValue] = useState(subject.getValue());

  if (subscriptionRef.current) {
    // unsubscribe in each rerender.
    subscriptionRef.current.unsubscribe();
  }

  useEffect(() => () => subscriptionRef.current?.unsubscribe(), []);

  return function getValue() {
    if (!subscriptionRef.current) {
      subscriptionRef.current = subject.subscribe(() => {
        setValue(subject.getValue());
      });
    }
    return subject.getValue();
  };
}

Using this lazy‑subscription Hook in a component with a switch statement can dramatically reduce unnecessary renders, as only the branches that actually need the external value will subscribe.

The article also shows how the Hook can be used to obtain the latest form data without triggering a re‑render of a submit button, further illustrating performance gains.

In summary, the new Hook introduces lazy subscription, finer‑grained scheduling, and the ability to work in both legacy and concurrent modes, promising a potential "Hook revolution" that improves React application performance.