Brace Your React, New Core Web Vitals are Coming

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In a few months, Google will DESTROY your React app...

...well, kinda. In March, Google is releasing a new Core Web Vital called Interaction to Next Paint (INP). It measures the speed of interactions – and every React site Ivan has seen so far had INP way in red. This is bad for any site that cares about SEO.

In this talk, let’s learn how to prepare for the new Core Web Vital: how INP works, and how to improve it – both manually and with new React APIs like useTransition() and React Concurrency.

Ivan Akulov
Ivan Akulov
30 min
08 Dec, 2023

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  • Narges Haeri
    Narges Haeri
    Aspiring Professional
    Thank you so much for such an awesome content.

Video Summary and Transcription

The Talk discusses the NextPaint metric, a new performance metric introduced by Google that measures the speed of clicks or keyboard input on a page. It explores how React rendering can impact the NextPaint metric and offers optimization techniques such as using the useTransition hook in React 18. The Talk also covers the changes introduced in React 18's rendering process, the impact of wrapping with suspense, and the replacement of the First Input Delay metric with the interaction to the next page. The limitations of useTransition and general React performance optimization strategies are also discussed.

Available in Español

1. Introduction to NextPaint Metric

Short description:

Let's start with two bad news. First, there are no Rack Server components in this talk. Second, the interaction to NextPaint metric is a new performance metric introduced by Google. It measures how fast clicks or keyboard input are on the page. This metric becomes a core vital in March 2024. Let's dive into theory by covering the interaction, the interaction to NextPaint, and the interaction to NextPaint for the page. In a React app, the filtering notes interaction is slow, causing the spinner to freeze for a second.

All right, so let's start the talk with two bad news. The first one is that if you came to the talk for Rack Server components, there are not going to be any Rack Server components in this talk. They did not fit in. The second bad news is that we, as Rack developers, are bleeped. They would ban me otherwise if I said the word. But this is the PageSpeed Insights Report for newyorktimes.com. You can see that all of these performance metrics are green except the interaction to NextPaint.

This is the PageSpeed Insights Report for target.com, a big American e-commerce written in React just like newyorktimes.com. All PageSpeed Insights metrics are green except the interaction to NextPaint. This is the Notion website. Again, all these feed metrics are green except interaction to NextPaint. This metric, interaction to NextPaint, is a new performance metric introduced by Google. It measures how fast clicks or keyboard input are on the page. And in almost every React app or website I've seen so far, this metric is yellow or red. And also, this metric becomes a core vital in March 2024, which means that just in a few months, your CTO, your browser, your marketing team will also become suddenly aware that this metric is yellow or red.

Now, who here has worked with this metric before? Has anyone tried optimizing it? I saw one hand. Okay. Well, then let's take a really quick dive into theory. And to talk about theory, we would need to cover three things, the interaction, the interaction to NextPaint, and the interaction to NextPaint for the page. So, here is a React app. It's a simple note taking app. I could take notes. I can't see actually if I'm typing. I can take notes. I can open notes. I can create new notes. And I can filter notes. And the filtering notes interaction is slow. If you look at the spinner that spins in this corner, which spins when the page is idle, which freezes when the page also freezes, you would see that whenever I type into the filter, the spinner freezes for a second. And this is a slow interaction, and this is what makes the interaction to NextPaint bad.

2. Understanding Interaction to NextPaint

Short description:

I don't know how this interaction affects NextPaint. To understand, I install the Web Vitals extension from the Chrome Web Store. By enabling console logging, I can see the duration of each interaction on the page. The slowest interaction becomes the NextPaint metric, which can cause issues in the future. Google derives this metric by collecting INP values from websites.

Now, I can feel that this interaction is slow, but I don't know how actually this interaction is slow. I don't know, I don't know how actually it affects interaction to NextPaint. I don't know anything about interaction to NextPaint, right?

So, one thing I really like to do to see how fast interactions are and to see how they affect these new metric that Google has introduced is I like to go to the Chrome Web Store, install the Web Vitals extension. Go back to the app with the red paper. I'm running. Open extensions. Oh, wow. I cannot see from here. Oh, yeah. I can see. Hold on. I need to open the Web Vitals set. Let me do it differently. Yeah, I cannot see where the second one is. So, yeah, this is better. So, I need to open the extension settings. I need to enable console logging. Save settings and then open the console.

And at the moment I do that, and the moment I try doing anything in the app, I would see the extension log every interaction I make on the page. Like whenever I click something, I would see how long that click took. Whenever I type something, I would see how long that typing took. And whenever I try to type into my filter input, I would see how long that filtering action took. I would see that every time I type into the filter input, my interaction takes 700, 600 milliseconds. And I could see that as the interaction goes higher and higher, so does the INP interaction to an explained value also does.

So, what interaction to an explained basically is the new performance metric that Google introduced is it's the slowest interaction that happens on the page during a single user visit. So, I'm a user, I go to an app, I do a bunch of interactions in the app, I click stuff, I type stuff. And the slowest key press, the slowest click out of this is going to become the interaction to an explained metric that Google measures. That's going to be yellow or red, and that's going to create a lot of issues for us in just a few months. So, now, this was the interaction to an explained just for a single visit, but what Google shows is the interaction to an explained for the whole page. So, how does Google derive this number? The way it works is if you opted into sharing data with Google, what Google actually does is every time you go to any website and click on the website, Google collects every INP value from that website.

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