Mastering React’s useTransition: Smooth UI Updates Without Blocking the Main Thread

Introduction:
A few days ago, I was diving into rendering strategies in React and Next.js, discussing CSR, SSR, SSG, and ISR. One comment really caught my eye:

“useEffect ❌, useTransition ✅”

This got me curious—how can we make our React apps feel instantly responsive even under heavy state updates? That’s where useTransition shines. Let’s break it down and see how to use it effectively.

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1. Why We Need useTransition
In complex React apps, updating state in big components (like large lists, dashboards, or filtered tables) can block the main thread. Typing, clicking, or scrolling feels sluggish. Traditional useEffect updates can cause noticeable lag because React treats them as urgent updates.

useTransition (introduced in React 18) lets us mark some updates as transitions, which are non-urgent. React can then prioritize keeping the UI responsive while handling heavier updates in the background.

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2. Basic Usage

import { useState, useTransition } from 'react';

function SearchList({ data }) {
  const [query, setQuery] = useState('');
  const [filtered, setFiltered] = useState(data);
  const [isPending, startTransition] = useTransition();

  const handleChange = (e) => {
    const value = e.target.value;
    setQuery(value);
    startTransition(() => {
      const result = data.filter(item => item.includes(value));
      setFiltered(result);
    });
  };

  return (
    <div>
      <input type="text" value={query} onChange={handleChange} />
      {isPending && <p>Loading...</p>}
      <ul>
        {filtered.map((item, idx) => (
          <li key={idx}>{item}</li>
        ))}
      </ul>
    </div>
  );
}

Explanation:

• isPending: true while the transition is in progress
• startTransition: wraps state updates we want to defer
• Result: typing remains smooth, even for large lists

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3. When to Use useTransition

• Typing/search in large datasets
• Filtering or sorting heavy lists
• Updating dashboards with multiple components
• UI interactions that must stay responsive

4. Best Practices

• Don’t overuse: simple state toggles don’t need transitions
• Combine with React.memo to avoid unnecessary re-renders
• Use with Suspense for async updates to show loaders

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5. Real-World Example

Imagine a product catalog with 1000+ items. Without useTransition, typing in a search bar blocks the UI. With useTransition:

• Typing stays fluid
• Filtered results update progressively
• Optional “Loading…” feedback via isPending

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6. Measuring Improvements

• Use React Profiler to see which components re-render
• Check Core Web Vitals for interactive performance
• Verify that deferred updates don’t compromise UX

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Conclusion:
useTransition is simple but powerful. It prioritizes UX over raw computation speed, making apps feel smoother and more professional. Next time your React app feels sluggish during large updates, consider marking some updates as transitions—you might be surprised by the difference.

CTA:
Have you tried useTransition yet? Share your experiences or tricky edge cases in the comments—I’d love to hear how you make your React apps feel lightning-fast!