?? Mastering React Hooks: A Beginner's Guide to useLayoutEffect

?? Promo

Now that we’ve tackled managing side effects with useEffect, let’s dive into situations where DOM updates must occur before the screen refreshes for a seamless user experience.

?? What is useLayoutEffect?

useLayoutEffect is a React hook that executes synchronously after all DOM mutations and before the browser paints the screen. It is ideal for tasks requiring DOM measurements or immediate updates.

?? How Does It Work?

useLayoutEffect works similarly to useEffect but runs synchronously. This means it "blocks the browser from painting" until the effect has run.

Example:

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

function ResizableBox() {
  const boxRef = useRef();
  const [boxWidth, setBoxWidth] = useState(0);

  useLayoutEffect(() => {
    const width = boxRef.current.getBoundingClientRect().width;
    setBoxWidth(width); // Updates state before painting

    return () => console.log("clean up ????");

  }, []); // ?? Dependency Array

  return (
    <div>
      <div ref={boxRef} style={{ width: '50%', border: '1px solid black' }}>
        Resize Me!
      </div>
      <p>Box Width: {boxWidth}px</p>
    </div>
  );
}        

How it works:

The useLayoutEffect hook measures the box width before the browser paints, ensuring accurate updates are reflected instantly.

? Good Practices

Use useLayoutEffect only when strict synchronization is required, such as DOM measurements or recalculations.

useLayoutEffect(() => {
  const dimensions = ref.current.getBoundingClientRect();
  setDimensions(dimensions);
}, []);        

? Bad Practices

• ? Avoid heavy computations in useLayoutEffect, as it blocks the browser paint, potentially causing performance bottlenecks.
• ? Don’t use it unnecessarily for tasks that can be handled with useEffect.

?? When and Why to Use useLayoutEffect

Use useLayoutEffect when you need to:

• Measure DOM dimensions or positions.
• Adjust styles or perform layout recalculations based on DOM properties.
• Synchronize animations where precise timing matters.

Why use it?

useLayoutEffect ensures your updates are applied immediately after the DOM changes, preventing visual glitches.

?? Key Points to Remember

Synchronous Execution

Unlike useEffect, useLayoutEffect runs before the browser paints, ensuring the DOM is updated before the user sees it.

• Blocking Nature

It delays rendering until the logic is executed, so use it sparingly.

• Similar Syntax to useEffect

The syntax and behavior (e.g., dependency arrays, cleanup functions) are identical to useEffect.

?? Difference Between useEffect and useLayoutEffect

?? useEffect

Execution:- runs asynchronously after rendering. It doesn't block the browser paint.

UseCase:- General side effects (e.g., API calls).

Performance Impact:- Does not blocks the rendering

?? useLayoutEffect

Execution:- runs synchronously before painting, making it ideal for DOM measurements or immediate updates.

UseCase:- DOM measurements or layout adjustments.

Performance Impact:- Blocks the rendering (Use with caution).

?? Tip

Prefer useEffect over useLayoutEffect unless absolutely necessary. Use tools like React DevTools to identify and optimize slow renders caused by overusing useLayoutEffect.

?? Summary

useLayoutEffect is a powerful tool for scenarios requiring precise DOM updates before rendering. While it resembles useEffect in usage, its synchronous execution makes it a specialized hook for specific use cases.

?? Conclusion

Understanding when to use useLayoutEffect can drastically improve your app’s responsiveness and visual accuracy. Use it wisely to ensure a balance between precision and performance.

?? What Next

Now that we’ve mastered handling DOM updates before the browser paints, let’s explore a hook that helps us fetch and manage data efficiently within our components. Can you guess the next hook? if yes let me know in the comments ??.