StrictMode helps catch bugs and prepare for future React features. Here's how to use it.
Basic Usage
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What StrictMode Does
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Detecting Impure Renders
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Effect Cleanup Testing
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Detecting Deprecated APIs
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Detecting Legacy Context
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Common Issues and Fixes
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State Initialization
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Production Behavior
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Best Practices
Enable StrictMode:
✓ Wrap entire app for new projects
✓ Enable for new features
✓ Address warnings before shipping
✓ Use for migration to newer React
Fix Common Issues:
✓ Add cleanup to all effects
✓ Make renders pure
✓ Use AbortController for fetches
✓ Avoid side effects in initializers
Testing:
✓ Test that effects handle remounting
✓ Verify subscriptions clean up
✓ Check for memory leaks
✓ Test with concurrent features
Avoid:
✗ Disabling to hide warnings
✗ Side effects during render
✗ Relying on effect timing
✗ Ignoring deprecation warnings
Conclusion
StrictMode is essential for catching bugs and preparing for React's concurrent features. The double-invoking behavior helps find missing cleanups and impure renders. Always enable StrictMode during development and address all warnings before production.