Optimizing Re-Rendering in React: Why It Matters and How to Do It

React is a powerful and popular JavaScript library for building user interfaces, particularly single-page applications where performance and responsiveness are critical. One of the core concepts in React is the component lifecycle, and a key part of this is rendering and re-rendering components. While React is highly efficient, unnecessary re-renders can still lead to performance issues, making optimization crucial.

Why Optimize Re-Renders in React?

1. Performance

Unnecessary re-renders can slow down your application. When a component re-renders, React must reconcile the virtual DOM with the actual DOM, which, although efficient, still consumes resources. Optimizing re-renders helps keep the application fast and responsive, ensuring a smoother user experience.

2. User Experience

A laggy interface can frustrate users. By minimizing re-renders, you can reduce latency and improve the overall user experience. This is especially important for applications with complex UIs or real-time updates, where responsiveness is key.

3. Resource Efficiency

Optimizing re-renders reduces CPU and memory usage, which is particularly beneficial for mobile devices and low-power hardware. Efficient resource use can also help in lowering operational costs in cloud-based applications.

4. Scalability

As your application grows, managing performance becomes increasingly challenging. Optimizing re-renders helps maintain performance as new features and components are added, ensuring scalability.

How to Optimize Re-Renders in React

1. Use React.memo

React.memo is a higher-order component that memoizes the result of a component’s render. This means that if the props have not changed, the component will not re-render.

import React from 'react';

const MyComponent = React.memo(({ name }) => {
  console.log('Rendering MyComponent');
  return <div>Hello, {name}!</div>;
});

export default MyComponent;

2. Use shouldComponentUpdate and PureComponent

For class components, you can use shouldComponentUpdate to control when a component re-renders. Alternatively, PureComponent automatically implements a shallow comparison of props and state.

import React, { PureComponent } from 'react';

class MyComponent extends PureComponent {
  render() {
    console.log('Rendering MyComponent');
    return <div>Hello, {this.props.name}!</div>;
  }
}

export default MyComponent;

3. Avoid Anonymous Functions in JSX

Anonymous functions in JSX can cause unnecessary re-renders because they are recreated on each render.

// Avoid this
<button onClick={() => handleClick()}>Click me</button>

// Use this
const handleClick = () => {
  // handle click
};
<button onClick={handleClick}>Click me</button>

4. Use useCallback and useMemo

In functional components, useCallback and useMemo can be used to memoize functions and values, respectively, preventing unnecessary re-renders.

import React, { useCallback, useMemo } from 'react';

const MyComponent = ({ name, age }) => {
  const memoizedValue = useMemo(() => computeExpensiveValue(age), [age]);
  const memoizedCallback = useCallback(() => {
    console.log(name);
  }, [name]);

  return (
    <div>
      <div>{memoizedValue}</div>
      <button onClick={memoizedCallback}>Click me</button>
    </div>
  );
};

export default MyComponent;

5. Properly Manage State

Keep state local to the component that needs it. Lifting state too high can cause unnecessary re-renders of parent components and their children.

// Less efficient
const ParentComponent = () => {
  const [value, setValue] = useState(0);

  return (
    <div>
      <ChildComponent value={value} />
      <button onClick={() => setValue(value + 1)}>Increment</button>
    </div>
  );
};

// More efficient
const ParentComponent = () => {
  return (
    <div>
      <ChildComponent />
    </div>
  );
};

const ChildComponent = () => {
  const [value, setValue] = useState(0);

  return (
    <div>
      <div>{value}</div>
      <button onClick={() => setValue(value + 1)}>Increment</button>
    </div>
  );
};

6. Use Immutable Data Structures

Immutable data structures make it easier to determine when a state change has occurred, aiding in more efficient re-renders.

const newState = {...oldState, key: 'newValue'};

Conclusion

Optimizing re-renders in React is essential for maintaining performance, providing a smooth user experience, using resources efficiently, and ensuring scalability. By employing techniques such as React.memo, PureComponent, useCallback, and properly managing state, you can significantly enhance the performance of your React applications. Keeping these best practices in mind will help you build more efficient and scalable React applications, ensuring a better experience for your users.

Comments

[Mayank Tamrkar]

Valuable content .

[Hari Bhandari]

Regarding point 3. handleClick will be re-created every render unless it's outside of the component or memoized using useCallback.

[Will Stone]

And don’t useCallback every function, especially small arrow functions. It’ll be a DX mess and can actually result in less performance when overused. The upcoming React 19 release will optimise this for you.

So while 3 is good code organisation practice, this tip doesn’t optimise for rerenders.

[Hari Bhandari]

@wstone I am not in favor of using useCallback un-necessarily but was just point out that point 3 doesn't optimize for re-renders.

[Will Stone]

Agreed. I was building on your point 😊