ReactJS

Improving INP in React and Next.js

Published Apr 19, 2024

Updated Apr 19, 2024

5 min read

Improving INP in React and Next.js

In one of my previous articles, I've explained what INP is, how it works, and how it may affect your website. I also promised you to follow up with more concrete advice on how to improve your INP in your favorite framework. This is the follow-up article, where I'll focus on how to improve your INP score in React and Next.js.

How to prepare for INP in React and Next.js?

The first thing to do is to ensure you're using the latest version of React. The React team has been working on making React more INP-friendly and has already made some improvements in the latest versions.

To enhance your INP score, consider fully taking advantage of new features introduced in React 18, such as Concurrent Rendering, Automatic Batching, and Selective Hydration. However, there are also some general areas to focus on, such as SSR and SSG in Next.js, Web Workers, or optimizing your hooks and state management.

Concurrent Rendering

The Concurrent Mode in React uses an algorithm that breaks rendering down into so-called "fiber nodes" and schedules the renders based on their expiration and priority. This effectively allows the user to interact with the page while the rendering is still in progress.

In previous React versions, all updates, such as setState calls were treated as "urgent" and once the re-render had started, there was no way to interrupt it. Concurrent Mode changes this by being able to prioritize the updates and interrupt a non-blocking state update started with startTransition. For a simple explanation of concurrency in React, you can check out Dan Abramov's explanation.

As part of the Concurrent Mode, React introduced several lifecycle methods that allow you to prioritize the rendering of certain parts of your UI, such as:

useTransition hook that allows you to update the state without blocking the UI,
useDeferredValue hook that allows you to defer the rendering of certain parts of your UI,
startTransition API that, similarly to the useTransition hook lets you mark a state update as non-blocking. It lacks, however, an indication of whether it's still pending.

Automatic Batching

Introduced in React 18, Automatic Batching reduces the number of re-renders that happen on state changes even when they happen outside of event handlers, e.g. in a setTimeout or Promise callback. This feature comes out of the box and you don't have to do anything to enable it, and it makes a great argument for upgrading to React 18.

Selective Hydration

Selective Hydration allows you to take hydration off the main thread by wrapping your components in a Suspense boundary. This way, components can become interactive faster as the browser can do other work on the main thread while the hydration is happening.

To fully take advantage of selective hydration, consider the following:

Prioritizing Above-the-Fold Content: Use Suspense boundaries strategically around any parts of your application that may take the server longer to deliver to ensure they don’t block critical content from becoming interactive as soon as possible.
Hydration on Interaction: Implementing hydration upon user interaction for non-critical components can drastically reduce the main thread's workload, enhancing INP.

Vercel even has a small case study showing how using selective hydration improved the performance of a Next.js site.

Server-Side Rendering (SSR) and Static Site Generation (SSG) in Next.js

Not everything has to run client-side. Next.js excels in SSR and SSG capabilities, which can significantly impact INP by delivering content to users faster. Optimizing SSR with techniques like incremental static regeneration (ISR) or leveraging SSG for static pages ensures that users can interact with content faster, improving the perceived performance.

Workers

Offloading heavy computations to Web Workers can free up the main thread, enhancing the responsiveness of React and Next.js applications. This strategy is especially useful when dealing with third-party scripts. Offloading such scripts in Next.js can be easily done by specifying the "worker" strategy on your Script component. Be aware that this feature is not yet stable and does not work with the app directory, though.

If you want to take things one step further, you could use Partytown, which helps you offload any resource-intensive scripts to Web Workers. It comes with a React component that you can use to wrap your third-party scripts and offload them to a Web Worker, and it's compatible with Next.js as well.

Hooks and State Management

State management in React applications can easily get out of hand, leading to unnecessary re-renders and effectively an increased INP. Sometimes, using a state management library like Redux or MobX can help you consolidate your state and reduce the number of re-renders. However, they are not silver bullets and can also introduce performance issues if not used properly.

If you are dealing with a lot of re-renders due to prop changes, make sure you are leveraging memoization. As of now, you may need to work with useMemo and useCallback hooks to memoize your values and functions, respectively. The upcoming React 19’s Forget Compiler, however, will apparently memoize everything under the hood, making these hooks obsolete. Using memoization properly can help you reduce the number of re-renders and improve your INP. To investigate your hook dependencies and re-renders, you can leverage React Developer Tools or use this handy helper hook I found on the internet to trace your re-renders:

import { useRef, useEffect } from "react";

export function useTraceUpdate(props: any) {
  const prev = useRef(props);
  useEffect(() => {
    const changedProps = Object.entries(props).reduce((ps: any, [k, v]) => {
      if (prev.current[k] !== v) {
        ps[k] = [prev.current[k], v];
      }
      return ps;
    }, {});
    if (Object.keys(changedProps).length > 0) {
      console.log("Changed props:", changedProps);
    }
    prev.current = props;
  });
}

Conclusion

Improving INP in React and Next.js is not easy and can require much investigation and fine-tuning. Still, it's worth doing to avoid being penalized by Google in its search results and provide a better experience for your users.

Adopting React 18's new features, leveraging SSR and SSG in Next.js, utilizing Web Workers, and optimizing hooks and state management can significantly boost your INP score and deliver a faster application to your users. Remember, INP is just one among many performance metrics emphasizing the need for a comprehensive approach to performance optimization

This Dot is a consultancy dedicated to guiding companies through their modernization and digital transformation journeys. Specializing in replatforming, modernizing, and launching new initiatives, we stand out by taking true ownership of your engineering projects.

We love helping teams with projects that have missed their deadlines or helping keep your strategic digital initiatives on course. Check out our case studies and our clients that trust us with their engineering.

About the author(s)

Jan Kaiser
Software engineer passionate about everything web-related. Particularly loves Angular, SCSS, TypeScript, soccer and dachshunds
@honzikec @honzikec

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Improving INP in React and Next.js

Improving INP in React and Next.js

How to prepare for INP in React and Next.js?

Concurrent Rendering

Automatic Batching

Selective Hydration

Server-Side Rendering (SSR) and Static Site Generation (SSG) in Next.js

Workers

Hooks and State Management

Conclusion

Jan Kaiser

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