Using useDeferredValue in React

React 18 introduced a new hook called useDeferredValue, which allows you to defer the update of a value until the next render. This can be particularly useful when you have a computationally expensive operation or a value that frequently changes, but you don't want to block the rendering of your component.

The primary use case for useDeferredValue is to improve performance by prioritizing the rendering of the most important parts of your application while deferring less critical updates. It helps in avoiding unnecessary calculations and rendering cycles, leading to a smoother user experience.

How useDeferredValue works

useDeferredValue is designed to work in conjunction with the Suspense component and the new React concurrent mode. It allows you to specify a value that should be deferred and updated lazily during the next render.

Here's an example of how you can use useDeferredValue:

1import React, { useState, useMemo, useDeferredValue } from 'react';
2
3function ExpensiveComponent() {
4    const [value, setValue] = useState<string>('');
5    const deferredValue = useDeferredValue(value);
6
7    const list = useMemo(() => {
8        const dataList: string[] = [];
9        for (let i: number = 0; i < 10000; i++) {
10            dataList.push(deferredValue);
11        }
12        return dataList;
13    }, [deferredValue]);
14
15    return (
16        <div>
17            <input value={text} onChange={(e) => setValue(e.target.value)} />
18            <ul>
19                {list.map((item) => (
20                    <li key={item}>{item}</li>
21                ))}
22            </ul>
23        </div>
24    );
25}

In the example above, the value prop is deferred using useDeferredValue. This means that any changes to value will not immediately trigger a re-render of the component. Instead, the update will be scheduled and applied during the next render.

Benefits of useDeferredValue

The use of useDeferredValue offers several benefits:

• Performance optimization: By deferring updates of less critical values, you can ensure that rendering is focused on the most important parts of your application, improving overall performance.
• Smoothing user interactions: Deferring updates can help prevent janky or stuttering UI caused by frequent updates or expensive calculations.
• Simplified code: useDeferredValue provides an intuitive and declarative way to handle deferring updates, reducing the need for manual optimizations and workarounds.

Considerations and limitations

While useDeferredValue can be a powerful tool, it's important to keep a few things in mind:

• Concurrency mode requirement: useDeferredValue requires React concurrent mode and should be used within a Suspense boundary.
• Delayed updates: Since updates are deferred, there might be a slight delay between when the value changes and when the component reflects the updated value.
• Selective usage: Not all values should be deferred. It's important to consider the impact of deferring a value and determine if it's suitable for your specific use case.

Conclusion

The introduction of useDeferredValue in React 18 brings an effective way to improve performance and user experience by deferring less critical updates. By selectively deferring values, you can optimize your application's rendering and ensure a smoother interaction for your users.