A Deep Dive into useInsertionEffect in React

In the vast world of React hooks, a new addition titled useInsertionEffect has made its debut, providing unique capabilities for those working with CSS-in-JS libraries. However, it's crucial to understand the intent behind this hook, its best use cases, and potential pitfalls to make the most of it. Let's dive in.

What is useInsertionEffect?

useInsertionEffect is a React hook designed primarily for CSS-in-JS library authors. It allows for the insertion of elements into the DOM before any layout effects are triggered. If you're not working on a CSS-in-JS library and need a location to inject styles, you might be better off with useEffect or useLayoutEffect.

Reference Syntax:

Usage:

For injecting dynamic styles from CSS-in-JS libraries, call useInsertionEffect to insert styles before any effects that might read layout:

Key Parameters:

• setup: This is the function that contains your effect's logic. When your component is introduced to the DOM, React will execute this setup function before firing any layout effects. Moreover, if there are any changes in the dependencies after a re-render, React will execute the cleanup function, if provided.

• dependencies (optional): This refers to all reactive values referenced in the setup code. Examples include props, state, and other component body variables. If these aren't specified, your effect will re-run after every component re-render.

Returns:

useInsertionEffect returns nothing (undefined).

Important Caveats:

1. Effects only run on the client and are excluded during server rendering.
2. State updates are forbidden within useInsertionEffect.
3. At the time useInsertionEffect runs, refs aren't attached.
4. The exact timing for when the DOM updates after useInsertionEffect is unpredictable.
5. Unlike other effects, the cleanup and setup functions in useInsertionEffect interleave, meaning they execute one component at a time.

Rethinking CSS-in-JS

Traditional React component styling utilizes plain CSS:

But some developers are now leaning towards CSS-in-JS, where styles are authored directly in JavaScript. The three common approaches are:

1. Static extraction to CSS files via a compiler.
2. Inline styles, such as <div style={{ opacity: 1 }}>
3. Runtime injection of <style> tags.

However, for those opting for runtime <style> tag injection, it's essential to be aware of the potential pitfalls. Runtime injection can force frequent browser recalculations and can be inefficient if executed at an inopportune time in React's lifecycle. useInsertionEffect offers a solution for the latter concern by allowing styles to be inserted before layout effects trigger.

Deep Dive: The Benefits Over Other Methods

One might wonder, why not just inject styles during rendering or use useLayoutEffect?

If you choose to insert styles while rendering, and React is processing a non-blocking update, the browser will recalibrate the styles repeatedly as it renders a component tree. This can drastically slow performance.

On the other hand, useInsertionEffect trumps over useLayoutEffect or useEffect for style insertion because it ensures that all <style> tags are already in place before any other effects run in your components. This guarantees that layout calculations are accurate and not based on outdated styles.

Conclusion

useInsertionEffect is a robust addition to React's hooks arsenal, especially for those diving into CSS-in-JS territories. By understanding its nuances, developers can harness its potential to optimize style injection, ensuring smoother and more efficient applications. Always ensure you're using the right tool for the job!