What is the use of useLayoutEffect in React?

What is the use of useLayoutEffect in React?

The useLayoutEffect hook in React is used to perform side effects that need to happen synchronously after all DOM mutations. It's similar to useEffect, but it fires synchronously after all DOM updates, which can be useful for reading layout from the DOM and synchronously re-rendering.

When should I prefer useLayoutEffect over useEffect?

You should prefer useLayoutEffect when you need to read layout information and make changes before the browser has a chance to paint. For example, if you need to measure the size of an element and then apply styles based on that measurement, useLayoutEffect is the right choice.

Can you give an example of useLayoutEffect in action?

Sure! Here's a simple example:

import React, { useLayoutEffect, useRef } from 'react';

function Example() {
  const boxRef = useRef(null);

  useLayoutEffect(() => {
    const box = boxRef.current;
    console.log('Box dimensions:', box.getBoundingClientRect());
  });

  return <div ref={boxRef} style={{ width: '100px', height: '100px' }}>Box</div>;
}

In this example, useLayoutEffect logs the dimensions of the box after it has been rendered.

Are there any performance considerations with useLayoutEffect?

Yes, since useLayoutEffect runs synchronously after DOM updates, it can block the browser's painting process. This can lead to performance issues if used excessively or with heavy computations. It's best to use it only when necessary.