React hooks have revolutionized the way developers write code in React. One such hook is useDeferredValue, which is a relatively new addition to the React API, introduced in React version 18. This hook is particularly useful for optimizing the rendering performance of components that have expensive computations or I/O operations.

In this article, we will explore the useDeferredValue hook, understand its purpose, and see how it can be used with a simple example.

What is useDeferredValue?

The useDeferredValue hook is used to defer the update of a state value until the next render cycle. In other words, when you update the value using setState, the new value will not immediately be reflected in the component's state. Instead, React will wait until the next render cycle to apply the update.

The primary use case for useDeferredValue is to optimize the rendering performance of components that have expensive computations or I/O operations. By deferring the state update, we can ensure that the expensive operation is only performed when it is absolutely necessary, i.e., when the component is actually being rendered.

How to use useDeferredValue?

To use the useDeferredValue hook, we first need to import it from the React package:

import { useDeferredValue } from 'react';

Next, we create a state variable using the useState hook:

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

We can then use the useDeferredValue hook to defer the update of the value:

`const deferredValue = useDeferredValue(value);`

Finally, we can use the deferredValue variable in our component's render method:

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

In the above example, we are using the useDeferredValue hook to defer the update of the value state variable. We are then using the deferredValue variable in our component's render method to display the current value.

When the user clicks the "Increment" button, the setValue function is called to update the value state variable. However, since we are using the useDeferredValue hook, the update is deferred until the next render cycle.

Here's another example of how to use the useDeferredValue hook:
Let's say we have a component that renders a list of users fetched from an API. In this example, we are using the useEffect hook to fetch the data and store it in state:

import { useEffect, useState} from 'react';

export function App() {
  const [users, setUsers] = useState([]);

  useEffect(() => {
    async function fetchData() {
      const response = await fetch(
        'https://jsonplaceholder.typicode.com/users'
      );
      const data = await response.json();
      setUsers(data);
    }
    fetchUser();
  }, []);

  return (
    <>
      <ul>
        {users.map((user) => (
          <li key={user.id}>{user.name}</li>
        ))}
      </ul>
    </>
  );
}

In this example, every time the component re-renders, the fetchData function is called, and a request is made to the API. This can result in unnecessary requests being made if the component is re-rendered multiple times before the data is actually displayed.

To optimize this component using the useDeferredValuehook, we can modify the code as follows:

import { useEffect, useState, useDeferredValue } from 'react';

export function App() {
  const [users, setUsers] = useState([]);
  const deferredUsers = useDeferredValue(users);

  useEffect(() => {
    async function fetchData () {
      const response = await fetch(
        'https://jsonplaceholder.typicode.com/users'
      );
      const data = await response.json();
      setUsers(data);
    }
    fetchUser();
  }, []);

  return (
    <>
      <ul>
        {deferredUsers.map((user) => (
          <li key={user.id}>{user.name}</li>
        ))}
      </ul>
    </>
  );
}

In this modified example, we are using the useDeferredValue hook to defer the update of the users state variable. This means that even if the component re-renders multiple times before the data is actually displayed, the fetchData function will only be called once, when the data is actually needed.

This can help to reduce the number of unnecessary requests being made to the API and improve the overall performance of the component.

Benefits of useDeferredValue

The useDeferredValue hook can be a powerful tool for optimizing the performance of your React components. By deferring state updates, you can ensure that expensive computations or I/O operations are only performed when they are absolutely necessary, i.e., when the component is actually being rendered.

In addition, useDeferredValue can also be used to prevent unnecessary re-renders. When a state update is deferred, React can compare the current and previous state values to determine whether a re-render is actually necessary. This can help to reduce the number of unnecessary re-renders in your application, improving its overall performance.

Conclusion

The useDeferredValue hook is a powerful tool for optimizing the performance of your React components. By deferring state updates, you can ensure that expensive computations or I/O operations are only performed when they are absolutely necessary, i.e., when the component is actually being rendered. This can help to improve the overall performance of your application and reduce unnecessary re-renders.