How to Use useDeferredValue Hook in React

This article provides a practical guide on how to implement the useDeferredValue hook in React to optimize application performance. You will learn what the hook does, when to use it over traditional debouncing, and how to implement it step-by-step with a clear code example to keep your user interface responsive during heavy rendering tasks.

What is useDeferredValue?

The useDeferredValue hook is a built-in React hook introduced in React 18. It allows you to defer updating a non-urgent part of your UI, keeping the main interaction (like typing in an input field) smooth and responsive.

Instead of blocking the user interface while rendering a slow component, React will render the urgent update first (the input value) and then render the deferred value in the background.

When Should You Use It?

You should use useDeferredValue when: * You have a CPU-intensive rendering task (such as filtering a large list) that slows down the user interface. * You want to avoid showing a loading spinner and instead prefer to keep showing the old UI until the new UI is ready. * You cannot optimize the slow component further, and throttling or debouncing is not the ideal user experience.

Step-by-Step Implementation

To implement useDeferredValue, pass the state variable you want to defer into the hook. Then, use the returned deferred value in your expensive rendering logic.

1. Import the Hook

First, import useDeferredValue and useState from React.

import { useState, useDeferredValue, useMemo } from 'react';

2. Set Up Your State and Deferred Value

Create your primary state (e.g., search query) and pass it to useDeferredValue.

const [query, setQuery] = useState('');
const deferredQuery = useDeferredValue(query);

3. Pass the Deferred Value to the Slow Component

Use the deferredQuery for your heavy computational task or pass it down to the list component. To prevent unnecessary re-renders of the slow component while typing, wrap the slow component in React.memo or wrap the rendering logic in useMemo.

Here is a complete, working example:

import { useState, useDeferredValue, useMemo, memo } from 'react';

// An expensive component that slows down rendering
const SlowList = memo(({ query }) => {
  const items = [];
  for (let i = 0; i < 250; i++) {
    items.push(<div key={i}>Result {i} for "{query}"</div>);
  }
  return <div>{items}</div>;
});

export default function SearchApp() {
  const [query, setQuery] = useState('');
  // Defer the query update
  const deferredQuery = useDeferredValue(query);

  const handleChange = (e) => {
    setQuery(e.target.value);
  };

  return (
    <div style={{ padding: '20px' }}>
      <input 
        type="text" 
        value={query} 
        onChange={handleChange} 
        placeholder="Type to search..." 
      />
      {/* 
        The input updates instantly, while the SlowList 
        waits for the deferredQuery to update in the background.
      */}
      <SlowList query={deferredQuery} />
    </div>
  );
}

Key Considerations