useLayoutEffect runs synchronously after DOM mutations but before the browser paints. Here's when and how to use it.
useEffect vs useLayoutEffect
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When to Use useLayoutEffect
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DOM Measurements
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Scroll Position
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Animation Initialization
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Focus Management
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Canvas and WebGL
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Third-Party Libraries
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Server-Side Rendering
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Performance Considerations
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Custom Hooks with useLayoutEffect
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Best Practices
When to Use useLayoutEffect:
✓ DOM measurements
✓ Scroll position management
✓ Preventing visual flicker
✓ Synchronous animations
✓ Third-party DOM libraries
When to Use useEffect:
✓ Data fetching
✓ Subscriptions
✓ Logging
✓ Any async operation
✓ Most side effects
Performance:
✓ Keep useLayoutEffect fast
✓ Avoid expensive computations
✓ Don't block with async code
✓ Prefer useEffect when possible
SSR:
✓ Use isomorphic version
✓ Handle client-only cases
✓ Suppress warnings appropriately
Conclusion
useLayoutEffect runs synchronously before the browser paints, making it essential for DOM measurements and preventing visual flicker. Use it sparingly for synchronous DOM operations like measuring elements, managing scroll position, or initializing animations. For most side effects, useEffect is the better choice as it doesn't block the browser. Remember to handle SSR cases with an isomorphic version.