What is the useDeferredValue hook?

The useDeferredValue hook is used to defer updating a part of the UI to keep other parts responsive. It accepts a value and returns a "deferred" version of that value that may lag behind. This is useful for optimizing performance when rendering expensive components.

#### Syntax

     const deferredValue = useDeferredValue(value);
     

#### Example: Search with Deferred Results

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

     function SearchResults({ query }) {
       // Expensive computation or large list filtering
       const results = useMemo(() => {
         return largeDataSet.filter(item => 
           item.name.toLowerCase().includes(query.toLowerCase())
         );
       }, [query]);

       return (
         <ul>
           {results.map(item => <li key={item.id}>{item.name}</li>)}
         </ul>
       );
     }

     function SearchPage() {
       const [query, setQuery] = useState('');
       const deferredQuery = useDeferredValue(query);
       const isStale = query !== deferredQuery;

       return (
         <div>
           <input 
             value={query} 
             onChange={(e) => setQuery(e.target.value)}
             placeholder="Search..."
           />
           <div style={{ opacity: isStale ? 0.5 : 1 }}>
             <SearchResults query={deferredQuery} />
           </div>
         </div>
       );
     }
     

The input stays responsive while the expensive SearchResults component re-renders with a slight delay using the deferred value.