Exploring useDeferredValue in React 18: A Comprehensive Guide

React 18 introduced several innovative features to enhance the performance and user experience of React applications. One such feature is the useDeferredValue hook. This hook is designed to help manage state updates by deferring non-urgent updates, ensuring that the application remains responsive even under heavy load. In this article, we’ll delve into what useDeferredValue is, why it’s useful, and how to use it effectively with practical examples.

What is useDeferredValue?

useDeferredValue is a hook in React 18 that allows you to defer a state value until the main updates are completed. This hook is particularly useful for optimizing performance in scenarios where immediate updates aren’t necessary, such as when rendering a large list of items based on user input.

Key Features of useDeferredValue

1. Deferred State Updates: It defers the value update, allowing the UI to remain responsive by prioritizing more urgent updates.
2. Improved Performance: Helps in reducing the load on the main thread by deferring non-critical updates.
3. Enhanced User Experience: By deferring updates, it ensures that the application remains responsive and provides a smoother user experience.

Why Do We Need useDeferredValue?

React applications often deal with complex state updates that can impact performance, especially when dealing with large data sets or heavy computations. Without deferring non-critical updates, the UI can become unresponsive, leading to a poor user experience. useDeferredValue addresses this by allowing developers to defer less critical state updates, ensuring that the application remains fast and responsive.

Example Scenarios

1. Filtering Large Lists: When filtering a large list based on user input, immediate updates can cause performance issues. Deferring the update helps keep the UI responsive.
2. Updating Charts or Graphs: In applications with dynamic charts or graphs, deferring updates ensures smooth transitions and interactions.
3. Form Validations: When performing complex validations on form inputs, deferring updates can improve the performance of the application.

How to Use useDeferredValue

Let’s explore how to use useDeferredValue with a practical example.

Example: Filtering a Large List

Consider an application where you need to filter a large list of items based on user input. Immediate updates can cause performance issues, but using useDeferredValue, we can defer the update and keep the UI responsive.

import React, { useState, useDeferredValue } from 'react';
const items = Array.from({ length: 10000 }, (_, index) => `Item ${index + 1}`);
function App() {
  const [query, setQuery] = useState('');
  const deferredQuery = useDeferredValue(query);
  const filteredItems = items.filter(item => item.toLowerCase().includes(deferredQuery.toLowerCase()));
  const handleChange = (e) => {
    setQuery(e.target.value);
  };
  return (
<div>
      <input type="text" value={query} onChange={handleChange} placeholder="Filter items" />
<ul>
        {filteredItems.map((item, index) => (
<li key={index}>{item}</li>
        ))}
      </ul>
</div>
  );
}
export default App;

Explanation

1. State Management: We have two pieces of state, query for the search input and deferredQuery for the deferred value.
2. Deferring the Query: The useDeferredValue hook defers the query value, ensuring that the filtering operation is performed after the main updates.
3. Filtering the List: The list is filtered based on the deferred query, which reduces the impact on performance and keeps the UI responsive.
4. Handling Input Change: When the user types into the input field, the handleChange function updates the query state, which is then deferred using useDeferredValue.

Example: Updating a Large Table

In another scenario, consider a large table that needs to be updated based on user actions. Without deferring updates, the UI might become unresponsive during the update process.

import React, { useState, useDeferredValue } from 'react';
const generateData = (rows) => Array.from({ length: rows }, (_, rowIndex) => ({
  id: rowIndex + 1,
  name: `Name ${rowIndex + 1}`,
  value: Math.random() * 100,
}));
const initialData = generateData(10000);
function DataTable() {
  const [data, setData] = useState(initialData);
  const deferredData = useDeferredValue(data);
  const handleUpdate = () => {
    const newData = data.map(item => ({
      ...item,
      value: Math.random() * 100,
    }));
    setData(newData);
  };
  return (
<div>
      <button onClick={handleUpdate}>Update Table</button>
<table>
<thead>
<tr>
<th>ID</th>
<th>Name</th>
<th>Value</th>
</tr>
</thead>
<tbody>
          {deferredData.map(item => (
<tr key={item.id}>
<td>{item.id}</td>
<td>{item.name}</td>
<td>{item.value.toFixed(2)}</td>
</tr>
          ))}
        </tbody>
</table></div>
  );
}
export default DataTable;

Explanation

1. State Management: The component manages a large set of data representing the table rows.
2. Deferring Data Updates: The useDeferredValue hook defers the data value, ensuring that the table updates do not block the main thread.
3. Handling Updates: When the “Update Table” button is clicked, handleUpdate triggers the update of the table data.
4. Rendering the Table: The table is rendered based on the deferred data, which helps maintain a responsive UI during updates.

By deferring non-urgent state updates, it helps ensure that the UI remains smooth and responsive, even during heavy computations or large data updates. Whether you’re filtering large lists, updating complex tables, or managing any heavy operations, useDeferredValue can significantly enhance the user experience of your React applications.