What is the useDeferredValue Hook in React?

The useDeferredValue hook is a React Hook introduced in React 18 that helps optimize application performance by deferring the re-rendering of non-urgent parts of the user interface. This article explores how useDeferredValue works, provides a practical implementation example, and explains how it differs from traditional optimization techniques like debouncing and throttling.

What is useDeferredValue?

useDeferredValue accepts a state value and returns a “deferred” version of that value. When the original value changes rapidly (for example, as a user types into a search input), React will prioritize updating the urgent UI (the input field itself) and delay updating the non-urgent UI that relies on the deferred value (such as a large, slow-rendering search results list).

const deferredValue = useDeferredValue(value);

During the initial render, the returned deferred value will be the same as the value you passed in. During updates, React will first attempt a render with the old deferred value, and then perform the deferred render with the new value in the background.

How It Works in Practice

Imagine a scenario where a user types into an input field, and each keystroke triggers a heavy computation or renders a long list of filtered items. Without optimization, the input field will lag because the browser is blocked by rendering the heavy list.

By using useDeferredValue, you can keep the input highly responsive:

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

function SlowList({ text }) {
  // Assume this component is artificially slowed down
  const items = useMemo(() => {
    const list = [];
    for (let i = 0; i < 250; i++) {
      list.push(<div key={i}>Result {i} for "{text}"</div>);
    }
    return list;
  }, [text]);

  return <div>{items}</div>;
}

export default function App() {
  const [query, setQuery] = useState('');
  const deferredQuery = useDeferredValue(query);

  return (
    <div>
      <input 
        type="text" 
        value={query} 
        onChange={(e) => setQuery(e.target.value)} 
        placeholder="Search..."
      />
      {/* The list receives the deferred value */}
      <SlowList text={deferredQuery} />
    </div>
  );
}

In this example, as the user types, query updates immediately, allowing the input field to reflect the keystrokes without lag. The deferredQuery lags behind slightly, updating only when React has free resources to process the heavy SlowList component.

useDeferredValue vs. Debouncing and Throttling

While useDeferredValue shares goals with debouncing and throttling, it works differently because it is deeply integrated into React’s concurrent rendering engine:

No Fixed Delay: Debouncing and throttling use a fixed delay (e.g., waiting 300ms after the user stops typing). useDeferredValue has no fixed delay. It starts rendering the deferred update immediately after the critical UI updates are painted. On faster devices, the deferral is barely noticeable; on slower devices, it dynamically adjusts to keep the UI responsive.
Interruptible Rendering: If the deferred value is rendering in the background and the user types another character, React will abandon the current background render and start a new one with the latest value. Traditional debouncing cannot interrupt a render once it has started.

When Should You Use It?

You should consider using useDeferredValue when:

You have performance bottlenecks caused by slow component re-renders that cannot easily be optimized.
You want to keep input fields responsive while updating content that depends on those inputs.
You cannot use useTransition because the state update is driven by a third-party library or prop changes from a parent component, rather than your own local state-setting functions.