Unveiling the use of useLayoutEffect in React

React provides various hooks to manage side effects, and while useEffect is commonly used, useLayoutEffect is a lesser-known but powerful tool. In this blog, we’ll explore its wonders and understand when and why to use it.

What is useLayoutEffect?

useLayoutEffect is similar to useEffect, but it fires synchronously after all DOM mutations and before the browser paints the screen. This makes it useful for scenarios where you need to measure or manipulate the DOM before the user sees any changes.
Key Differences Between useEffect and useLayoutEffect

Feature	useEffect	useLayoutEffect
Execution Timing	Runs asynchronously after the render is committed to the screen	Runs synchronously after DOM updates but before the paint
Suitable for	Side effects like data fetching, subscriptions	DOM measurements, animations, and layout adjustments
Performance	Less blocking; browser paints first	Can block rendering if overused

When to Use useLayoutEffect

Reading Layout and Making Adjustments
- If you need to measure an element’s size and update the state accordingly, use useLayoutEffect to ensure the measurement is taken before the paint.
Synchronous DOM Updates
- If you need to apply styles dynamically or manipulate the DOM immediately after a render, useLayoutEffect prevents flickering issues.
Animations and Transitions
- Helps in making smooth animations by ensuring layout calculations are accurate before the browser paints.

Example: Resizing an Element Without Flickering

import React, { useState, useLayoutEffect, useRef } from "react";

const Box = () => { const boxRef = useRef(null); const [width, setWidth] = useState(0);

useLayoutEffect(() => { if (boxRef.current) { setWidth(boxRef.current.offsetWidth); } }, []);

return ( <div ref={boxRef} style={{ width: "50%", padding: "20px", background: "lightblue" }}> Box width: {width}px ); };

export default Box;

When Not to Use useLayoutEffect

Avoid using it for data fetching or async operations, as it can block rendering.
Overuse may lead to performance issues if not handled properly.
If the side effect doesn’t require DOM measurement, useEffect is the better choice.

Conclusion

While useEffect is the go-to hook for handling side effects, useLayoutEffect plays a crucial role in managing synchronous DOM updates. Understanding when to use it can improve UI performance and enhance user experience. Use it wisely, and your React components will be smoother and more efficient!