useDeferredValue in React

Expert-Level Explanation

useDeferredValue is another hook in React that is used to defer the re-rendering of a non-urgent part of the UI. It takes a value and returns a new copy of the value that may "lag behind" the original one. This hook is useful when there's a piece of state that drives both urgent and non-urgent updates, and you want to ensure that the urgent updates (like user inputs) are not delayed.

Creative Explanation

useDeferredValue is like an office worker who handles two types of tasks: urgent and non-urgent. The worker prioritises urgent tasks (like responding to important emails) and handles non-urgent tasks (like filing paperwork) in their spare time. This way, the most critical tasks are always completed first, maintaining overall efficiency.

Practical Explanation with Code

Using useDeferredValue:

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

function ListComponent({ list }) {
  const [filter, setFilter] = useState('');
  const deferredFilter = useDeferredValue(filter);

  const filteredList = list.filter(item => item.includes(deferredFilter));

  return (
    <div>
      <input type="text" value={filter} onChange={(e) => setFilter(e.target.value)} />
      <ul>{filteredList.map(item => <li key={item}>{item}</li>)}</ul>
    </div>
  );
}

In this example, useDeferredValue is used to defer the filtering of the list, ensuring that typing in the input remains fast and responsive.

Real-World Example

A real-time dashboard displaying stock market data, useDeferredValue could be used to manage updates to complex visualisations or charts. While the dashboard fetches and processes new data (urgent), the less critical UI updates like rendering charts or graphs can be deferred, ensuring the dashboard remains responsive.