Unlocking Efficient State Updates in React

The Power of Batched Updates

When working with React, you’ve likely encountered situations where updating your component’s state triggers multiple re-renders. This can lead to performance issues and make your application feel sluggish.

By default, React batches updates made within event handlers or lifecycle methods, reducing the number of re-renders. However, when updates are made within callbacks like Promises or SetTimeout, React updates the state synchronously, leading to multiple re-renders.

A Real-World Example

Consider a scenario where you have two state values, item1 and item2, and you update their values when either of two buttons is clicked.

const initialState = {
  item1: '',
  item2: '',
};

function MyComponent() {
  const [state, setState] = useState(initialState);

  const handleClick1 = () => {
    Promise.resolve().then(() => {
      setState({ item1: 'New value 1' });
      setState({ item2: 'New value 2' });
    });
  };

  const handleClick2 = () => {
    setState({ item1: 'New value 1' });
    setState({ item2: 'New value 2' });
  };

  return (

  );
}

When you click the first button, which updates the state within a Promise, the component re-renders twice. But when you click the second button, which updates the state within an event handler, the component re-renders only once.

Forcing Batched Updates

To overcome this limitation, you can wrap your state update calls in ReactDOM.unstable_batchedUpdates(). This ensures that React batches the updates, resulting in only one re-render.

const handleClick1 = () => {
  Promise.resolve().then(() => {
    ReactDOM.unstable_batchedUpdates(() => {
      setState({ item1: 'New value 1' });
      setState({ item2: 'New value 2' });
    });
  });
};

While the method’s name might raise concerns about its stability, the React team has encouraged its use in production.

When to Use Batched Updates

Before reaching for unstable_batchedUpdates(), take a step back and assess whether you can refactor your code to make fewer state update calls. In many cases, multiple calls can be replaced with a single call.

• Refactor your code to make fewer state update calls.
• Consider using currying to compose the update values.

Hooks and Batched Updates

The concept of batched updates also applies to Hooks. When using multiple state objects in a functional component, it may be a sign that the component is violating the Single Responsibility Principle.

• Consider combining the state objects.
• Separate them into independent components.

By understanding when to use unstable_batchedUpdates() and refactoring your code to minimize state update calls, you can create faster and more efficient React applications.