Using React.memo to Avoid Unnecessary Renders

1. Introduction

This tutorial is aimed at teaching you how to utilize React.memo to avoid unnecessary re-renders in your React applications. React.memo is a higher-order component (HOC) that you can use to optimize your functional components if they render the same result given the same props.

Goals of this Tutorial

• Learn how to use React.memo to prevent unnecessary renders
• Understand when to use React.memo
• Learn how to memoize components with React.memo

Prerequisites

• Basic understanding of React and JavaScript
• Knowledge of functional components and React Hooks would be beneficial

2. Step-by-Step Guide

React.memo is a higher-order component that memorizes the output of a component and only re-renders it when the props change.

When to use React.memo?

You should consider using React.memo when you have a functional component that is often re-rendered with the same props. Memoizing the component can prevent unnecessary renders and improve overall performance.

How does React.memo work?

React.memo compares the current props and the next props using a shallow comparison. If the comparison results in no changes, React reuses the memoized component instead of re-rendering it.

Best Practices and Tips

• React.memo should be used judiciously. Overuse can lead to worse performance as memoization isn't free. It has its cost, and that's memory.
• React.memo is not suitable for components that have a complex render output, as the cost of memoization could exceed the benefits.

3. Code Examples

Basic Usage of React.memo

// A functional component
const MyComponent = React.memo(function MyComponent(props) {
  /* render using props */
});

// is equivalent to:
const MyComponent = function(props) {
  /* render using props */
};
export default React.memo(MyComponent);

Example

import React from 'react';

// Component
const MyComponent = React.memo((props) => {
  console.log('Component rendered');
  return <div>{props.count}</div>;
});

// Parent Component
export default function App() {
  const [count, setCount] = React.useState(0);

  return (
    <div>
      <MyComponent count={count} />
      <button onClick={() => setCount(count + 1)}>Increase</button>
    </div>
  );
}

In this example, 'Component rendered' will only log when the button is clicked and the count state changes. However, if there were any other state changes in the App component that caused a re-render, MyComponent would not re-render if the count prop hadn't changed.

4. Summary

We've learned how to use React.memo to prevent unnecessary re-renders of components in our React applications. Remember that React.memo should be used judiciously as overuse can lead to memory overhead.

5. Practice Exercises

1. Create a functional component that receives a prop. Use React.memo to prevent it from re-rendering when the prop doesn't change.
2. Create a parent component that has multiple child components. Some of the children should be memoized with React.memo, and others shouldn't. Experiment with state changes in the parent component and observe the difference in re-rendering between the memoized and non-memoized children.
3. Create a complex application with several components. Use React.memo to optimize the components that are often re-rendered with the same props. Test the application's performance before and after using React.memo.

Remember, practice makes perfect! The more you utilize React.memo in your applications, the better you'll understand when and how to use it effectively. Happy coding!