Different Behavior between useTransition and useDeferredValue in React

Core Problem

When using React Hooks, the useTransition hook and useDeferredValue hook behave differently when interrupting high-priority state updates. This inconsistency can lead to unexpected UI behavior and performance issues.

Solution & Analysis

The key difference lies in how these hooks handle concurrent updates.

useTransition

useTransition is designed to not block the UI during transitions. It uses a worklet queue to manage the transition's execution, allowing for asynchronous updates without blocking the main thread. However, if the transition is ongoing and you update other states that are not part of the transition, it will interrupt the transition as expected.

On the other hand, when you constantly update states that are not in transition (e.g., updating the counter state before the transition finishes), it can cause a temporary UI freeze. This happens because React is re-rendering the component with the new state values, which can lead to unnecessary re-renders and potential performance issues.

import { useTransition } from '@reactjsi/react-hooks';

function Sandbox() {
  const [counter, setCounter] = React.useState(0);
  const [isTransitioning, setIsTransitioning] = React.useState(false);

  const transition = useTransition(isTransitioning, () => ({}), {
    animation: 'fade',
    children: 'Transitioning...',
  });

  React.useEffect(() => {
    if (!transition.isRunning) {
      setCounter(counter + 1);
    }
  }, [counter]);

  return (
    <div>
      <button onClick={() => setIsTransitioning(true)}>Start Transition</button>
      <PostTab />
      <Counter value={counter} onChange={(newCount) => setCounter(newCount)} />
    </div>
  );
}

In the above code, we have a Counter component that updates its state constantly. When the transition is not running, it updates the counter state immediately. However, when the transition is running, updating the counter state will interrupt the transition.

useDeferredValue

On the other hand, useDeferredValue attaches a value to the render() method, which means that it will always be interrupted until the render() method stops running or a new render is requested. This behavior ensures that updates are batched together and executed efficiently.

import { useDeferredValue } from '@reactjsi/react-hooks';

function Sandbox() {
  const [counter, setCounter] = React.useState(0);
  const deferredValue = React.useDeferredValue(counter);

  return (
    <div>
      <button onClick={() => setCounter(deferredValue + 1)}>Increment</button>
      <PostTab />
      <Counter value={deferredValue} onChange={(newCount) => setCounter(newCount)} />
    </div>
  );
}

In the above code, we use useDeferredValue to attach a value to the render() method. When we update the counter state and call setCounter(), it will batch the update together with any other updates that are attached to the render() method.

Conclusion

The different behavior between useTransition and useDeferredValue can be attributed to their design goals and implementation differences. While useTransition is designed to not block the UI during transitions, it may lead to temporary UI freezes if concurrent updates occur. On the other hand, useDeferredValue ensures that updates are batched together and executed efficiently by interrupting its value until the render() method stops running or a new render is requested.

To avoid unexpected behavior, consider using useTransition with caution when updating states concurrently, and use useDeferredValue for attaching values to the render() method.

Reference

• Source