Understanding the useTransition Hook in React 18: Complete Guide with Examples

React 18 introduced several new hooks to enhance performance and user experience, one of the most significant being useTransition. This hook is designed to improve the handling of asynchronous updates, making your React applications more responsive by deferring non-urgent updates. In this article, we will explore what useTransition is, how it works, and how to use it with practical examples.

What is useTransition?

useTransition is a hook in React 18 that helps manage the prioritization of state updates. It allows developers to mark certain state updates as non-urgent transitions, which can be deferred to keep the UI responsive. This is particularly useful for improving the user experience during heavy computations or updates that might otherwise cause the UI to become sluggish.

Key Features of useTransition

1. Deferred Updates: Non-urgent updates can be deferred, preventing them from blocking urgent updates like user inputs.
2. Pending State: The hook provides a boolean value indicating whether the transition is still pending, allowing for the display of loading indicators or other feedback to the user.
3. Improved Performance: By deferring less critical updates, useTransition helps maintain a smooth and responsive UI, even under heavy load.

How Does useTransition Work?

useTransition returns two values:

1. isPending: A boolean indicating whether the transition is ongoing.
2. startTransition: A function that triggers the transition.

Here’s the basic syntax:

const [isPending, startTransition] = useTransition();

Example Usage

Let’s walk through a practical example to see how useTransition can be used in a React application.

Example: Filtering a Large List

Imagine you have a large list of items that you need to filter based on user input. Without useTransition, filtering this list might cause the UI to freeze while the filtering operation is being performed. By using useTransition, you can defer the filtering operation, ensuring that the UI remains responsive.

import React, { useState, useTransition } from 'react';
const items = Array.from({ length: 10000 }, (_, index) => `Item ${index + 1}`);
function App() {
  const [query, setQuery] = useState('');
  const [filteredItems, setFilteredItems] = useState(items);
  const [isPending, startTransition] = useTransition();
  const handleChange = (e) => {
    const value = e.target.value;
    setQuery(value);
    startTransition(() => {
      const result = items.filter(item => item.toLowerCase().includes(value.toLowerCase()));
      setFilteredItems(result);
    });
  };
  return (
<div>
      <input type="text" value={query} onChange={handleChange} placeholder="Filter items" />
      {isPending && 
Loading...
}
<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 filteredItems for the filtered list of items.
2. Handling Input Change: When the user types into the input field, handleChange is triggered. This function updates the query state immediately.
3. Deferring the Filtering: The startTransition function is used to defer the filtering operation. This means the filtering logic runs as a non-urgent update, keeping the UI responsive.
4. Pending State: While the filtering is in progress, isPending is true, and we can display a loading indicator to inform the user.

Another Example: Updating a Large Table

Consider a scenario where you need to update a large table based on user actions. Without useTransition, the UI might become unresponsive during the update. By using useTransition, you can ensure that the table updates do not block user interactions.

import React, { useState, useTransition } 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 [isPending, startTransition] = useTransition();
  const handleUpdate = () => {
    startTransition(() => {
      const newData = data.map(item => ({
        ...item,
        value: Math.random() * 100,
      }));
      setData(newData);
    });
  };
  return (
<div>
      <button onClick={handleUpdate}>Update Table</button>
      {isPending && 
Updating...
}
<table>
<thead>
<tr>
<th>ID</th>
<th>Name</th>
<th>Value</th>
</tr>
</thead>
<tbody>
          {data.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. Handling Updates: When the “Update Table” button is clicked, handleUpdate triggers the update of the table data.
3. Deferring Updates: The startTransition function defers the data update operation, ensuring that the UI remains responsive during the update.
4. Pending State: The isPending value is used to show a loading indicator while the table is being updated.

The useTransition hook in React 18 is a powerful tool for improving the performance and responsiveness of your applications. By deferring non-urgent updates, it helps ensure that critical interactions remain smooth and responsive. Whether you are filtering large lists, updating complex tables, or performing any heavy computations, useTransition can be a valuable addition to your React toolkit. By understanding and leveraging this hook, you can create more performant and user-friendly applications.