React useLayoutEffect Hook

React’s useLayoutEffect hook is one of the most important and useful hooks in the React library. It is a more powerful version of the useEffect hook, allowing you to perform certain actions after the DOM has been updated. In this tutorial, we’ll discuss what the useLayoutEffect hook is, how it works, and some of its use cases.

What is useLayoutEffect?

useLayoutEffect is a hook that runs immediately after the DOM has been updated but before the browser has had a chance to paint those changes to the screen. This means that any changes made using useLayoutEffect will be visible to the user before the component is rendered.

The useLayoutEffect hook is similar to the useEffect hook, but there is one key difference between them. The useEffect hook is asynchronous, meaning it runs after the browser has painted the changes to the screen. This can delay the user seeing the changes, which can be problematic in some situations. On the other hand, the useLayoutEffect hook is synchronous, which means it runs before the browser paints the changes to the screen.

How does useLayoutEffect work?

The useLayoutEffect hook works by running a callback function immediately after the DOM has been updated but before the browser can paint those changes to the screen. This means that any changes made using useLayoutEffect will be visible to the user before the component is rendered.

Here’s an example of how you might use the useLayoutEffect hook to measure the height of an element:

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

function App() {
  const ref = useRef(null);
  const [height, setHeight] = useState(null);

  useLayoutEffect(() => {
    setHeight(ref.current.clientHeight);
  }, [ref.current]);

  return (
    <div ref={ref}>
      <p>The height of this element is: {height}px</p>
    </div>
  );
}

In this example, we’re using the useLayoutEffect hook to set the height state variable to the height of the element referenced by the ref variable. The useLayoutEffect hook takes a callback function as its first argument, which is called immediately after the DOM has been updated. In this callback function, we’re setting the height state variable to the height of the element using the clientHeight property.

We’re also passing the ref.current value as the second argument to the useLayoutEffect hook. This tells React to run the callback function every time the ref.current value changes.

When should you use useLayoutEffect?

You should use the useLayoutEffect hook when you need to perform actions that require access to the DOM immediately after it has been updated. This could include measuring the height or width of an element, setting the focus on an input field, or updating the position of an element on the page.

One common use case for the useLayoutEffect hook is when you need to calculate the size or position of an element to render other elements on the page. For example, if you need to render a tooltip that appears when the user hovers over an element, you might use the useLayoutEffect hook to calculate the position of the tooltip relative to the element.

Another use case for the useLayoutEffect hook is when you need to perform actions that require access to the DOM before the browser has had a chance to paint those changes to the screen. This could include updating an element’s state based on user interactions, such as scrolling or clicking.

It’s important to note that the useLayoutEffect hook should be used sparingly, as it can potentially cause performance issues. Because the hook is synchronous, any code inside it will block the browser from rendering changes to the screen until that code has finished executing. This can lead to janky or unresponsive user interfaces, especially on slower devices.

To avoid performance issues, it’s recommended that you only use the useLayoutEffect hook when you absolutely need it and try to keep the amount of work you do inside the hook to a minimum.

Conclusion

The useLayoutEffect hook is a powerful tool for performing actions immediately after the DOM has been updated, but before the browser has had a chance to paint those changes to the screen. It’s similar to the useEffect hook, but runs synchronously and can potentially cause performance issues if overused.

You should use the useLayoutEffect hook when you need to perform actions that require access to the DOM immediately after it has been updated, such as measuring the size or position of an element. However, it’s important to use the hook sparingly and keep the amount of work you do inside it to a minimum to avoid performance issues.

Scroll to Top