The Importance of Memoizing Expensive Computations with useMemo

In React, failing to memoize expensive computations can lead to significant performance issues. Here’s why you should use useMemo for costly calculations:

The Problem Without useMemo

When you perform expensive computations directly in your component body:

function MyComponent({ items }) {
  // This runs on every render
  const sortedItems = items.sort(complexSortAlgorithm);
  // ...
}

The computation runs on every render, even if the inputs haven’t changed.

The Solution: useMemo

import { useMemo } from 'react';

function MyComponent({ items }) {
  const sortedItems = useMemo(() => {
    return items.sort(complexSortAlgorithm);
  }, [items]); // Only recomputes when `items` changes
  // ...
}

Benefits of Memoization

1. Performance Optimization: Avoids unnecessary recalculations
2. Referential Stability: Returns the same reference when dependencies don’t change
3. Better Render Efficiency: Reduces time spent in renders

When to Use useMemo

• Complex calculations (sorting, filtering, transformations)
• Operations on large datasets
• Computations that would cause noticeable lag if repeated
• When the result is used in dependency arrays of other hooks