React useMemo Guide

useMemo memoizes expensive calculations, recomputing only when dependencies change. Here's how to use it effectively.

Best Practices#

Use useMemo When:
✓ Expensive calculations
✓ Referential equality matters
✓ Preventing child re-renders
✓ Deriving complex state

Don't Use When:
✗ Simple calculations
✗ Primitive values
✗ Computation is cheap
✗ Value isn't used in renders

Dependencies:
✓ Include all values used inside
✓ Use specific properties, not objects
✓ Consider dependency stability
✓ Use ESLint exhaustive-deps rule

Performance:
✓ Profile before optimizing
✓ Measure actual impact
✓ Consider component structure
✓ Don't over-optimize

useMemo optimizes performance by memoizing expensive calculations and maintaining referential equality. Use it for computationally heavy operations, when passing objects/arrays to memoized children, or when deriving complex state. Always include all dependencies and profile your app to ensure memoization actually helps. Remember: premature optimization is the root of all evil - measure first, optimize second.

React useMemo Guide

Basic Usage#

When to Use useMemo#

Dependencies#

useMemo vs useCallback#

Referential Equality#

Conditional Memoization#

Lazy Initialization#

Common Patterns#

When NOT to Use useMemo#

Debugging useMemo#

Best Practices#

Conclusion#

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