Understanding the Difference Between useTransition and useDeferredValue

Core Problem

When using React Hooks to manage state transitions, developers may notice a difference in behavior between useTransition and useDeferredValue. Specifically, when updating states that are not currently in transition, useTransition can cause UI blocking, while useDeferredValue does not exhibit this issue. In this article, we will explore the reasons behind these differences and provide guidance on how to optimize state transitions in React.

Solution & Analysis

The main difference between useTransition and useDeferredValue lies in their approach to managing state updates during a transition.

import { useState, useTransition } from 'react';

function Counter() {
  const [count, setCount] = useState(0);
  const transitions = useTransition();

  return (
    <div>
      <button onClick={() => setCount(count + 1)}>Increment</button>
      <p>Count: {count}</p>
      <Post />
      {transitions.state === 'pending' && (
        <div>Transition in progress...</div>
      )}
    </div>
  );
}

In the Counter component, we use useTransition to manage state updates. When the button is clicked, we increment the count state and trigger a transition using transitions.useUpdate. However, when we update other states that are not in transition (e.g., the Post component), it can cause UI blocking.

On the other hand, useDeferredValue does not exhibit this issue.

import { useState } from 'react';

function Post() {
  const [post, setPost] = useState('');
  const deferredValue = useState('Initial Value');

  return (
    <div>
      <input type="text" value={deferredValue[0]} onChange={(e) => setDeferredValue(e.target.value)} />
      <p>Post: {post}</p>
    </div>
  );
}

In the Post component, we use useDeferredValue to manage state updates. When the user types in the input field, we update the deferredValue state using setDeferredValue. This change is not reflected immediately and does not cause UI blocking.

The reason for this difference lies in how each hook handles state updates during a transition.

import { useTransition } from 'react';

function useTransition() {
  const [state, setState] = useState('idle');

  return (update) => {
    if (state === 'pending') {
      update(() => {
        setState('idle');
      });
    }
  };
}

useTransition blocks the UI when a transition is in progress and updates other states. This is because it waits for the transition to complete before updating the state.

In contrast, useDeferredValue defers state updates until the next frame.

import { useState } from 'react';

function useDeferredValue(initialValue) {
  const [value, setValue] = useState(initialValue);

  return (update) => {
    return () => {
      setValue(update);
    };
  };
}

When useDeferredValue updates a state, it defers the change until the next frame. This allows other states to be updated concurrently without causing UI blocking.

Conclusion

In conclusion, the difference between useTransition and useDeferredValue lies in their approach to managing state updates during a transition. While useTransition can cause UI blocking when updating states that are not in transition, useDeferredValue defers state updates until the next frame, allowing for concurrent updates without blocking the UI. By understanding these differences, developers can optimize their state transitions and create more responsive user interfaces.

Reference

• Source