React Transitions

What is useTransition?

The useTransition hook helps you keep your React app responsive during heavy updates.

It lets you mark some state updates as "non-urgent", allowing other, more urgent updates to happen first.

When to Use Transitions?

Use transitions when you have:

• A slow operation that might freeze the UI
• Updates that aren't immediately critical
• Search results that take time to display

Basic Example

Here's a simple example showing how to use transitions in a search feature:

import { useState, useTransition } from 'react';

function SearchBar() {
  const [text, setText] = useState('');
  const [results, setResults] = useState('');
  const [isPending, startTransition] = useTransition();

  const handleChange = (e) => {
    // Urgent: Update input right away
    setText(e.target.value);

    // Non-urgent: Update search results
    startTransition(() => {
      setResults(e.target.value);
    });
  };

  return (
    <div>
      <input value={text} onChange={handleChange} />
      {isPending ? (
        <p>Loading...</p>
      ) : (
        <p>Search results for: {results}</p>
      )}
    </div>
  );
}

In this example:

• The input field updates immediately (urgent update)
• The search results update is marked as a transition (non-urgent)
• The loading message shows while the transition is pending

Real-World Example

Here's a more practical example with a slow search feature:

import { useState, useTransition } from 'react';

function SearchResults({ query }) {
  // Simulate slow search results
  const items = [];
  if (query) {
    for (let i = 0; i < 1000; i++) {
      items.push(<li key={i}>Result for {query} - {i}</li>);
    }
  }
  return <ul>{items}</ul>;
}

function App() {
  const [input, setInput] = useState('');
  const [query, setQuery] = useState('');
  const [isPending, startTransition] = useTransition();

  const handleChange = (e) => {
    // Urgent: Update input field
    setInput(e.target.value);
    
    // Non-urgent: Update search results
    startTransition(() => {
      setQuery(e.target.value);
    });
  };

  return (
    <div>
      <input 
        type="text" 
        value={input} 
        onChange={handleChange} 
        placeholder="Type to search..."
      />
      {isPending && <p>Loading results...</p>}
      <SearchResults query={query} />
    </div>
  );
}

How this example works:

1. When you type in the input field, it updates immediately
2. The search results update is wrapped in startTransition
3. While the results are updating, isPending is true
4. The UI stays responsive even with many results

useTransition Hook

The useTransition hook returns two items:

• isPending: tells you if a transition is active
• startTransition: function to mark updates as transitions