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Advanced 20 min readModule: Module 6: Performance Optimization (useMemo, useCallback, memo)

Memoization with useMemo, useCallback & React.memo

Cache expensive computations and stabilize function references to prevent unnecessary child re-renders.

What You Will Learn in This Lesson

  • useMemo to cache expensive mathematical or filtering calculations
  • useCallback to maintain stable function references between renders
  • React.memo for shallow prop comparison on child components

Introduction & Core Concept

React re-renders a component and all its children whenever state or props change. Memoization hooks cache calculations and function references to bypass redundant work.
WHY DOES THIS MATTER IN THE REAL WORLD?

Filtering 10,000 items on every keystroke causes perceptible UI lag. useMemo ensures the filter runs only when the dataset or query changes.

useMemo & useCallback Integration

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function FilterList({ items, filterQuery }) {
  // Cached computation
  const filtered = React.useMemo(() => {
    return items.filter(i => i.title.toLowerCase().includes(filterQuery.toLowerCase()));
  }, [items, filterQuery]);
 
  // Stable function reference
  const handleDelete = React.useCallback((id) => {
    console.log("Delete item:", id);
  }, []);
 
  return <div>Filtered Count: {filtered.length}</div>;
}

Line-by-Line Technical Breakdown

1Do not overuse memoization for trivial computations, as hook overhead can exceed the cost of re-rendering.

Try It Yourself (Interactive Editor)

Modify the code in real-time and click Run to test live browser output and console logs.

Intelligent Code Runner & Live Sandbox[JAVASCRIPT]
JAVASCRIPT SOURCE EDITOR
Interactive Live Code

Industry Best Practices & Professional Standards

  • Measure performance with React Profiler before applying memoization.

Lesson Summary & Core Takeaways

  • Targeted memoization prevents UI lag in complex data-heavy components.