When building dynamic web or mobile apps, rendering long lists like chat histories, product catalogs, or data tables can significantly slow your app to a crawl. We’ve seen developers struggle with re-renders, laggy scrolling, and wasted performance. Here’s a quick, practical breakdown of how to optimize the rendering of a large list of items in React that makes rendering large lists smooth and efficient without sacrificing user experience.
Quick Takeaway
Optimizing list rendering in React isn’t about one magic fix; it’s a combination of memoization, stable props, virtualization, and smart architecture. Apply these techniques early, and your app will scale smoothly no matter how many items you throw at it.
What the Issue Is?
When working on a recent project, one of our developers faced a common challenge in React: rendering a list of nearly 1,000 complex components, each with its own internal state and props. The problem? Every time a single item was updated, the entire list re-rendered, leading to noticeable lag and poor user experience. Even though techniques like React.memo and useCallback were attempted, the performance gains were minimal because the memoization wasn’t applied correctly.
This scenario is something many businesses encounter. As an experienced app development company in Kochi, Kerala, we’ve learned that solving these issues requires a deeper understanding of how React handles rendering, props, and component identity.
How We Optimized Large List Rendering in React
When we ran into performance issues, we didn’t just look up fixes—we tested, refined, and built a process that now guides how we approach React performance in every project. Here’s what worked for us:
1. Use React.memo on the Item Component
Wrap the component itself, not the JSX call with React.memo. This stops unchanged list items from re-rendering.
jsx const Item = React.memo(({ value, onUpdate }) => { return <div>{value}</div>; }); |
2. Keep Callbacks Stable with useCallback
Functions recreate on every render unless memoized. Use useCallback to keep them stable and prevent downstream re-renders.
jsx const handleUpdate = useCallback((id) => { // update logic }, []); |
3. Pass Only What’s Needed
Instead of sending the full object, pass primitives like id, name, or value. Shallow comparison works best on simple props.
4. Use react-window or react-virtualized
Virtualization renders only what’s visible in the viewport. For lists in the thousands, this is the single biggest win.
Pro tip: If list items hold local state, remember that off-screen items may unmount. Persist state outside the list (e.g., in a map or store) or use a stable
5. Split Complex Items into Smaller Components
If a list item does a lot, break it down into smaller, memoized components. This localizes rendering work.
6. Avoid Inline Functions in JSX
Avoid Problematic Inline Functions in JSX
Inline functions like onClick={() => handleClick(id)} create new references every render.
- If the child is not memoized, this is fine.
- If the child is memoized, it can break memoization.
Use useCallback when passing functions to memoized children:
jsx const handleClick = useCallback((id) => { … }, []); <ItemMemoized onClick={handleClick} /> |
7. Batch State Updates
React 18 introduced automatic batching, so multiple setState calls inside async code, promises, or event handlers are grouped into one render. This reduces overhead when updating list-related state.
8. Lazy Load Data in Chunks
Don’t fetch or render everything at once. Implement infinite scrolling or “load more” to reduce initial rendering cost.
9. Profile with React DevTools
Identify bottlenecks instead of guessing. Often, it’s not the list itself but expensive child logic.
10. Keep Styles Lightweight
Heavy inline styles or CSS-in-JS can slow down long lists. Consider utility classes or lightweight styling solutions.
Prefer:
- Utility-first CSS (Tailwind, CSS Modules)
- Precompiled CSS-in-JS (Stitches, Vanilla Extract)
- Minimal inline styles for critical cases
The key prop is critical for React’s diffing algorithm. Unstable keys (like array indexes) cause unnecessary re-renders and can reset component state.
jsx {items.map((item) => ( <Item key={item.id} {…item} /> ))} |
Final Thoughts
Rendering large lists in React can be smooth—if you apply the right patterns from the start. Misusing React.memo, poorly structured props, and no virtualization are common pitfalls.
At Fegno, as a software development company based in Kerala, we integrate performance best practices into every React or cross-platform project. Whether you’re building web dashboards or mobile applications, thinking ahead about list rendering makes a difference in user experience and scalability.
Senior Front-End Developer at Fegno Technologies with 5+ years of experience crafting clean, responsive, and scalable web applications. Specialized in React.js, Next.js, JavaScript, HTML5, and CSS3, turning complex ideas into seamless digital experiences. Passionate about UI/UX excellence, performance optimization, and modern web technologies.
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