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React Hooks: When to Use useLayoutEffect Instead of useEffect

Brandon Evans 70

Photo by Kelly Sikkema on Unsplash

React Hooks revolutionized the way we manage state and side effects in React functional components. With hooks, we can write more concise and modular code, making it easier to understand and maintain our applications. One of the most commonly used hooks is useEffect, which allows us to perform side effects in our components. However, there are cases where we need to use a similar hook called useLayoutEffect. In this article, we'll explore when it's appropriate to use useLayoutEffect instead of useEffect in our React applications.

Understanding useEffect and useLayoutEffect

Before diving into the differences between the two hooks, let’s first understand what they do. Both useEffect and useLayoutEffect enable us to perform side effects in our functional components. A side effect refers to any operation that affects something outside the scope of the component, such as fetching data from an API, manipulating the DOM, or subscribing to events.

The primary difference between useEffect and useLayoutEffect lies in the timing of when they are executed. The useEffect hook schedules the side effect to be executed after the component has rendered and the browser has painted the changes on the screen. On the other hand, useLayoutEffect executes the side effect synchronously immediately after the DOM has been updated but before the browser has a chance to paint the changes.

In most cases, we can use useEffect without any issues. However, certain scenarios require us to use useLayoutEffect to ensure the side effect runs synchronously, allowing us to make changes to the DOM layout before it's painted.

Manipulating the DOM Layout

One of the primary use cases for useLayoutEffect is when we need to manipulate the DOM layout directly. Since useLayoutEffect runs before the browser paints the changes, it gives us the opportunity to make adjustments to the DOM layout that might affect subsequent renderings.

Let’s consider an example where we want to measure the dimensions of a DOM element and apply some styling based on those measurements. Here’s how we can achieve this using useLayoutEffect:

import { useLayoutEffect…