Use Deferred Value for Responsive UIs

The Problem: Sluggish UIs

Ever built a feature that feels great most of the time, but then grinds to a halt when you have a lot of data? Maybe a long list that needs filtering, or a search input that updates a complex UI in real-time. You type, and the UI freezes for a moment. It’s a bad user experience. We’ve all been there, both as developers and users.

This often happens because React re-renders are blocking. When a state update triggers a re-render, especially one involving heavy computation or a large number of DOM updates, it can take time. During that time, the browser can’t do anything else, including responding to user input like clicks or scrolling. The UI becomes unresponsive.

Enter useDeferredValue

React 18 introduced useDeferredValue which is a hook designed to help with this exact problem. Think of it as a way to tell React, “This update is important, but not immediately critical. You can postpone it if something more urgent, like user interaction, needs to happen first.”

How does it work? useDeferredValue takes a value and returns a deferred version of that value. When the original value changes, the deferred value won’t update immediately. Instead, React will try to update it in the background, after more important updates have been processed. This is particularly useful for expensive UI updates that are triggered by non-urgent state.

Let’s look at a common example: a search input that filters a large list.

Code Example: Search and Filter

Imagine you have a list of items and a search input. As the user types, you want to filter the list.

Without useDeferredValue, a direct state update might look like this:

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import React, { useState } from 'react';
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function MyListComponent({ items }) {
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  const [query, setQuery] = useState('');
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  const filteredItems = items.filter(item =>
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    item.name.toLowerCase().includes(query.toLowerCase())
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  );
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  return (
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    <div>
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      <input
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        type="text"
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        value={query}
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        onChange={e => setQuery(e.target.value)}
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        placeholder="Search items..."
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      />
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      <ul>
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        {filteredItems.map(item => (
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          <li key={item.id}>{item.name}</li>
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        ))}
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      </ul>
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    </div>
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  );
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}
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export default MyListComponent;

If items is very large, typing into the input can cause a noticeable lag because the filter operation and subsequent list re-render happen immediately after setQuery is called.

Now, let’s integrate useDeferredValue.

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import React, { useState, useDeferredValue } from 'react';
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function MyListComponent({ items }) {
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  const [query, setQuery] = useState('');
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  // Create a deferred version of the query
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  const deferredQuery = useDeferredValue(query);
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  // Filter using the deferred query. This update is less urgent.
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  const filteredItems = items.filter(item =>
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    item.name.toLowerCase().includes(deferredQuery.toLowerCase())
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  );
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  return (
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    <div>
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      <input
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        type="text"
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        value={query}
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        onChange={e => setQuery(e.target.value)}
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        placeholder="Search items..."
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      />
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      {/* Optionally, show a placeholder or the old list while filtering */}
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      {query !== deferredQuery && <p>Updating results...</p>}
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      <ul>
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        {filteredItems.map(item => (
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          <li key={item.id}>{item.name}</li>
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        ))}
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      </ul>
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    </div>
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  );
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}
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export default MyListComponent;

In this updated version, deferredQuery will lag behind query. When you type, setQuery updates query immediately, allowing the input to feel responsive. However, the filtering and list re-render will use deferredQuery. React prioritizes the input update. Once the main thread is free, it will process the deferred update. This means the list might show slightly stale results for a brief moment, but the UI remains interactive.

When to Use It?

useDeferredValue is best for non-critical UI updates that can tolerate a small delay.

• Filtering or searching large lists: As shown above.
• Expensive calculations that update the UI: If a calculation takes a long time and its immediate result isn’t essential for user interaction.
• Real-time updates that aren’t mission-critical: Like updating a complex graph based on live data.

It’s not suitable for:

• Input fields themselves: You want the input value to update immediately.
• Critical state updates: Any state that the user directly interacts with and expects an instant visual change.

Benefits

• Improved Perceived Performance: The UI feels faster because it stays responsive.
• Smoother User Experience: Prevents janky interactions and freezing.
• Simpler Logic: Often simpler than manual debouncing or throttling for UI updates.

Caveats

• Stale UI: The UI might show slightly outdated information temporarily. You might need to add visual cues (like a loading indicator) to manage user expectations.
• React 18+: This hook is only available in React 18 and later.

useDeferredValue is a powerful tool for making your React applications feel snappier. By strategically deferring less critical updates, you can ensure that your UI remains responsive, even when dealing with heavy data or complex rendering.