How to prevent unnecessary re-renders when passing callbacks to memoized child components?

Summary

The issue at hand is preventing unnecessary re-renders in a React application when passing callbacks to memoized child components. The problem arises because functions are re-created on every render, causing the prop reference to change, even if the props used inside the child don’t change. This leads to the child component re-rendering unnecessarily.

Root Cause

The root cause of this issue is:

• Functions being re-created on every render
• The prop reference changing due to the new function creation
• React.memo not being able to prevent re-renders due to the changed prop reference

Why This Happens in Real Systems

This issue occurs in real systems because:

• Functions are reference types and are re-created on every render
• React uses shallow comparison to check for prop changes
• Memoization is not effective when prop references change

Real-World Impact

The real-world impact of this issue is:

• Unnecessary re-renders can cause performance issues
• Increased memory usage due to the creation of new function instances
• Decreased user experience due to slower rendering times

Example or Code

import React, { useState, useCallback } from "react";

const Child = React.memo(({ onClick }) => {
  console.log("Child rendered");
  return Click;
});

export default function Parent() {
  const [count, setCount] = useState(0);
  const handleClick = useCallback(() => {
    console.log("Button clicked");
  }, []);

  return (
    

      
Count: {count}
       setCount(count + 1)}>Increment
      
    
  );
}

How Senior Engineers Fix It

Senior engineers fix this issue by:

• Wrapping callbacks with useCallback to prevent re-creation of functions
• Using dependencies in useCallback to ensure the function is only re-created when necessary
• Optimizing memoization by only memoizing components that have expensive render functions or are re-rendered frequently

Why Juniors Miss It

Juniors may miss this issue because:

• Lack of understanding of how functions are re-created on every render
• Insufficient knowledge of how React uses shallow comparison to check for prop changes
• Inexperience with optimizing performance in React applications, leading to premature optimization or overuse of memoization