? Deferred Values (useDeferredValue)

? Quick Overview

The useDeferredValue() hook helps React applications stay responsive by delaying updates to non-urgent UI parts. It is especially useful when rendering large lists or expensive components based on fast-changing inputs.

? Key Concepts

• Separates urgent updates from non-urgent rendering
• Improves typing and interaction responsiveness
• Works automatically without manual transitions
• Introduced in React 18

? Syntax / Theory

// useDeferredValue creates a deferred version of a value
const deferredValue = useDeferredValue(value);

• value → original rapidly changing value
• deferredValue → delayed value used for rendering

? Code Example: Deferred Search Results

This example demonstrates how typing remains smooth while a large list renders in the background.

// Demonstrates deferred rendering for large lists
import React, { useState, useDeferredValue } from "react";

function List({ input }) {
const deferredInput = useDeferredValue(input);
const items = Array(3000)
.fill("Item")
.map((x, i) => <li key={i}>{deferredInput} - {i}</li>);

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

export default function DeferredExample() {
const [text, setText] = useState("");

return (
<div>
<input
value={text}
onChange={(e) => setText(e.target.value)}
placeholder="Type something..."
/>
<List input={text} />
</div>
);
}

⚡ Live Interactive Demo

Try typing quickly in the box below. Notice that the Input updates instantly (urgent), while the List updates slightly later (deferred). We are rendering 5,000 items to simulate a heavy workload.

? Live Output / Explanation

As the user types, the input updates instantly while the list updates slightly later. This prevents the UI from freezing during expensive renders.

⚙️ How It Works

• React marks the deferred value as low priority
• Urgent updates render immediately
• Deferred rendering happens in the background
• Ensures smooth interactions in heavy UIs

? Interactive Understanding

Think of typing as a priority lane. The input field stays fast, while the heavy list rendering waits briefly. This separation keeps the application responsive.

? Use Cases

• Search bars with large datasets
• Filtering tables and grids
• Live analytics dashboards
• Complex charts and visualizations