One of the keys to building performant React applications is avoiding unnecessary re-renders. React's rendering engine is efficient, but it's still crucial to prevent re-renders where they aren't needed. In this post, we'll cover common mistakes and how to avoid them.

1. Memoizing Components Using React.memo

Memoization helps you skip re-renders when the component's props haven't changed. However, it's easy to misuse React.memo by not implementing a custom comparison function.

Incorrect Usage:

const MemoizedComponent = React.memo(MyComponent);

This only checks if the props reference has changed, which might not always be sufficient.

Correct Usage:

const MemoizedComponent = React.memo(MyComponent, (prevProps, nextProps) => {
  return prevProps.itemId === nextProps.itemId;
});

Here, we use a custom comparison function that only triggers a re-render when the itemId prop changes.

2. Avoid Excessive Use of Inline Functions

Using inline functions inside JSX can lead to unnecessary re-renders as React treats a new function as a new prop on every render.

Incorrect Usage:

function ButtonComponent() {
  return <button onClick={() => handleClick()}>Click me</button>;
}

This causes handleClick to be recreated on every render, leading to unnecessary re-renders.

Correct Usage:

import { useCallback } from 'react';

function ButtonComponent() {
  const handleClick = useCallback(() => {
    // Handle click logic
  }, []);

  return <button onClick={handleClick}>Click me</button>;
}

By using useCallback, we memoize the handleClick function, preventing unnecessary re-creation on each render.

3. Leveraging PureComponent

When working with class components, using React.PureComponent ensures that the component only re-renders if its props or state change. If you're using React.Component, it may lead to unnecessary re-renders.

Incorrect Usage:

class CardComponent extends React.Component {
  // Component logic
}

Correct Usage:

class CardComponent extends React.PureComponent {
  // Component logic
}

By extending React.PureComponent, React will shallowly compare props and state, avoiding needless re-renders.

4. Optimizing useSelector in Functional Components

When using useSelector from react-redux, it's important to select only the necessary slice of the state.

Incorrect Usage:

import { useSelector } from 'react-redux';

const DataComponent = () => {
  const globalState = useSelector((state) => state);
  // Render logic
};

This will cause the component to re-render whenever any part of the state changes.

Correct Usage:

import { useSelector } from 'react-redux';

const DataComponent = () => {
  const selectedData = useSelector((state) => state.specificSlice);
  // Render logic based on specific slice
};

By selecting only the necessary part of the state, you minimize re-renders.

5. Implementing shouldComponentUpdate in Class Components

For class components that don't extend PureComponent, manually implementing shouldComponentUpdate allows more granular control over when the component re-renders.

Incorrect Usage:

class ListItem extends React.Component {
  // Component logic
}

This will re-render every time the parent component renders, even if the props and state haven't changed.

Correct Usage:

class ListItem extends React.Component {
  shouldComponentUpdate(nextProps, nextState) {
    return this.props.itemId !== nextProps.itemId || this.state.value !== nextState.value;
  }

  // Component logic
}

By customizing shouldComponentUpdate, we ensure that the component only re-renders when the itemId prop or the value state changes.

Conclusion

By employing these techniques, you can significantly reduce unnecessary re-renders in your React applications, leading to better performance. Implementing memoization with React.memo, leveraging PureComponent, and fine-tuning shouldComponentUpdate are key strategies for optimizing your React components.

Understanding when and how to optimize rendering can greatly enhance user experience by providing faster and more responsive applications.

References:

1. GeeksforGeeks. (2023). What is Memoization in React?
2. Syncfusion. (2024). Memoization in React
3. Hygraph. (2024). What is React Memo and How to Use it?
4. Refine.dev. (2024). React Memo Guide with Examples

If you found this guide useful, please consider sharing it with others! 😊

This blog provides an updated and comprehensive overview of avoiding unnecessary re-renders in React applications while incorporating best practices and changing variable names for clarity and relevance in modern web development practices.

Citations:
[1] https://www.geeksforgeeks.org/what-is-memoization-in-react/
[2] https://stackoverflow.com/questions/74013864/why-arent-all-react-components-wrapped-with-react-memo-by-default
[3] https://www.syncfusion.com/blogs/post/what-is-memoization-in-react
[4] https://hygraph.com/blog/react-memo
[5] https://refine.dev/blog/react-memo-guide/
[6] https://dmitripavlutin.com/use-react-memo-wisely/
[7] https://www.topcoder.com/thrive/articles/memoization-in-react-js
[8] https://react.dev/reference/react/memo