Best Practices for Implementing useLayoutEffect in React
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Chapter 1: Introduction to useLayoutEffect
React offers two primary hooks for managing side effects: useEffect and useLayoutEffect. Both hooks share a similar structure and require a function that encapsulates the effect logic along with an optional dependency array. The key distinction lies in their execution timing: useEffect operates asynchronously after the browser renders the screen, whereas useLayoutEffect executes synchronously prior to rendering.
This variation significantly impacts how these hooks are utilized and the types of side effects they can handle. In this discussion, we'll delve into best practices for employing useLayoutEffect, complete with examples and practical applications.
Video Description: Learn how to effectively use the useLayoutEffect hook in React to optimize your components.
When to Choose useLayoutEffect
A general guideline is to favor useEffect over useLayoutEffect when feasible. This preference arises because useLayoutEffect can hinder the browser's rendering process, potentially leading to performance issues if the effect logic is complex or invoked too often. Conversely, useEffect runs post-rendering and does not impede the perceived loading speed for users.
Nonetheless, there are scenarios where useLayoutEffect is either necessary or advantageous compared to useEffect. These situations typically involve utilizing layout data for rendering or making synchronous DOM updates. Examples include:
- Assessing the dimensions or position of an element prior to its modification
- Animating an element based on its former or subsequent state
- Aligning the scroll positions of two distinct elements
- Modifying the DOM in ways that impact other elements
- Interacting with localStorage or sessionStorage
In such cases, utilizing useLayoutEffect guarantees that the effect logic executes before the browser renders the screen, preventing visual inconsistencies or flickering that could arise from using useEffect.
How to Effectively Use useLayoutEffect
Using useLayoutEffect is akin to using useEffect, but with a heightened awareness of performance and the frequency of effects. Here are some strategies for effective use:
- Implement a cleanup function to reverse any changes made by the effect. This practice helps prevent memory leaks and unintended side effects when the component unmounts or re-renders with different dependencies.
- Define a dependency array to restrict when the effect activates. This approach helps avoid unnecessary re-executions of the effect and enhances performance.
- Refrain from creating new objects or functions within the effect function or as dependencies. This can lead to excessive re-runs of the effect, negatively impacting performance. Instead, utilize constants, memoized values, or custom hooks to manage state updates and non-reactive logic externally.
- Use conditional rendering or early returns to bypass executing the effect when it is unnecessary. This helps minimize needless DOM mutations and boosts performance.
- Employ a ref to maintain a mutable value that doesn’t trigger a re-render upon changes. This can be beneficial for storing references to DOM elements, timer IDs, or any values pertinent solely to the effect logic.
Examples of Using useLayoutEffect
Let’s explore some practical examples of using useLayoutEffect in various scenarios.
Measuring Layout Before the Browser Repaints
A common application of useLayoutEffect is to measure an element's size or position before it changes due to a state update or prop change. For instance, consider implementing a collapsible panel component that animates its height during opening or closing transitions. We can leverage useLayoutEffect to gauge the height of the panel content before and after a change, applying a CSS transition accordingly.
import { useState, useRef, useLayoutEffect } from "react";
function CollapsiblePanel({ title, children }) {
const [isOpen, setIsOpen] = useState(false);
const contentRef = useRef(null);
useLayoutEffect(() => {
const content = contentRef.current;
const prevHeight = content.getBoundingClientRect().height;
content.style.height = "auto";
const nextHeight = content.getBoundingClientRect().height;
content.style.height = prevHeight + "px";
content.offsetHeight;
content.style.height = nextHeight + "px";
}, [isOpen]);
useLayoutEffect(() => {
return () => {
const content = contentRef.current;
if (content) {
content.style.height = "";}
};
}, []);
return (
<div onClick={() => setIsOpen((open) => !open)}>
{title} {isOpen ? "▲" : "▼"}
<div ref={contentRef}>{children}</div>
</div>
);
}
In this example, useLayoutEffect is employed to measure and adjust the height of the panel content element before and after it changes based on the isOpen state. A cleanup function is also used to reset the height upon component unmounting, ensuring a seamless transition effect.
Synchronizing Scroll Positions of Two Elements
Another application of useLayoutEffect is to synchronize the scroll positions of two independently scrolling elements. For example, imagine a table component with a fixed header and a scrollable body. We want to ensure that horizontal scrolling on either element keeps them aligned.
import { useRef, useLayoutEffect } from "react";
function Table({ columns, data }) {
const headerRef = useRef(null);
const bodyRef = useRef(null);
useLayoutEffect(() => {
const header = headerRef.current;
const body = bodyRef.current;
const handleHeaderScroll = () => {
body.scrollLeft = header.scrollLeft;};
const handleBodyScroll = () => {
header.scrollLeft = body.scrollLeft;};
header.addEventListener("scroll", handleHeaderScroll);
body.addEventListener("scroll", handleBodyScroll);
return () => {
header.removeEventListener("scroll", handleHeaderScroll);
body.removeEventListener("scroll", handleBodyScroll);
};
}, []);
return (
<div>
<div ref={headerRef}>
{columns.map((column) => (
<div key={column.key}>{column.label}</div>))}
</div>
<div ref={bodyRef}>
{data.map((row) => (
<div key={row.id}>
{columns.map((column) => (
<div key={column.key}>{row[column.key]}</div>))}
</div>
))}
</div>
</div>
);
}
In this case, useLayoutEffect is utilized to add scroll event listeners to both the header and body elements, while also incorporating a cleanup function to remove these listeners upon unmounting. This approach ensures the scroll positions remain in sync.
Conclusion
useLayoutEffect is advantageous for executing side effects that rely on or influence layout details or DOM mutations. Its best-suited applications include measuring layouts, animating elements, synchronizing scroll positions, and more.
However, it is advisable to prefer useEffect whenever possible, as useLayoutEffect can obstruct rendering and adversely affect performance. Use useLayoutEffect only when necessary for your user interface.
We hope this article enhances your understanding of how and when to effectively utilize the useLayoutEffect hook in React. If you found it helpful, feel free to show your appreciation and follow for more insights!
Video Description: Dive deeper into the useLayoutEffect hook with a comprehensive tutorial.