How React Compiler Performs on Real Code

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The most talked-about news in the React community this year is probably the React Compiler. Everyone is looking forward to being saved from the re-render plague and never having to write useCallback/useMemo again.


But are we truly there yet? Can the React Compiler actually achieve those things? Do we need to do anything other than turning it on and enjoying a re-render-free life? I ran it on a few real-world apps to find the answer. Want to see the results?


In this talk, we’ll take a look at what the React Compiler is, what problems it solves, and how it performs on simple code examples and real-world applications.

This talk has been presented at React Advanced 2024, check out the latest edition of this React Conference.

FAQ

React Compiler is a tool from the React team that aims to optimize re-renders by memoizing components, props, and dependencies of hooks by default. It plugs into the build system to improve performance by reducing unnecessary re-renders.

For most developers, enabling React Compiler may be sufficient, allowing them to forget about manual memoization. However, those needing to optimize every millisecond may still need to use manual memoization techniques.

Nadia has spent the last few years investigating performance, re-renders, and React. She has written articles, made YouTube videos, and published a book on these topics.

React Compiler does not transpile external libraries, so its effectiveness may vary depending on the library's compatibility with memoization.

Nadia found that React Compiler might not catch every re-render, especially with external libraries or complex legacy code. It may not handle cases where code isn't fine-tuned for memoization.

In large or old projects, it is advisable to enable the compiler gradually, file by file, and conduct thorough testing to ensure compatibility and performance improvements.

Memoization in React involves using React.memo to wrap components. It checks if props have changed; if not, re-renders are stopped. For non-primitive values, useMemo and useCallback hooks are used to preserve references and prevent re-renders.

Nadia is a developer who has worked for a small startup and Atlassian on the product JIRA. She loves to travel and moved from Australia to Austria. Her hobbies include investigating how things work and writing about them.

React Compiler has a minimal impact on initial load performance and can significantly improve interaction performance by reducing unnecessary re-renders.

Nadia starts with an idea, writes examples and articles, iteratively refines them, and discovers new insights during the process. She shares her findings through writing and presentations.

Nadia Makarevich
Nadia Makarevich
31 min
25 Oct, 2024

Comments

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  • Joaquin Bueno
    Joaquin Bueno
    Great Talk! been following Nadia's content for a couple of months now, always good stuff!
  • Guadalupe Lazzo
    Guadalupe Lazzo
    Nadia explained really well and took the time to test it with real scenarios. Super valuable thank you!
Video Summary and Transcription
I'm Nadia, a developer experienced in performance, re-renders, and React. The React team released the React compiler, which eliminates the need for memoization. The compiler optimizes code by automatically memoizing components, props, and hook dependencies. It shows promise in managing changing references and improving performance. Real app testing and synthetic examples have been used to evaluate its effectiveness. The impact on initial load performance is minimal, but further investigation is needed for interactions performance. The React query library simplifies data fetching and caching. The compiler has limitations and may not catch every re-render, especially with external libraries. Enabling the compiler can improve performance but manual memorization is still necessary for optimal results. There are risks of overreliance and messy code, but the compiler can be used file by file or folder by folder with thorough testing. Practice makes incredible cats. Thank you, Nadia!

1. Introduction and Background

Short description:

I'm Nadia, a developer with experience in performance, re-renders, and React. I've investigated these topics and shared my findings through articles, videos, and a book. Recently, the React team released the React compiler, which eliminates the need for memoization. I've tested the compiler on synthetic examples and real apps to evaluate its performance. Now, I'm excited to share my insights.

Thank you for the intro. As mentioned, my name is Nadia. Let me start by quickly introducing myself and talking a little bit about myself. I've been a developer for a very long time now. I worked for a small startup at some point. I worked for Atlassian for a few years on a product that some of you probably know and probably love called JIRM. I'm a bit lazy and also I love to travel. So a few years ago, I moved from Australia to Austria just because it's easier to spell. I'm a little bit of a nerd and one of my nerdy hobbies is to investigate how things work and then write the results down. I spent the last few years investigating everything that I could about performance, about re-renders, and React. I wrote a bunch of articles on this topic, I did YouTube videos, I even published a book, half of which is dedicated to the topic of re-renders, memoization, and how to control them. And during those years I kept seeing visitors from the future probably who would kindly inform everyone around them that memoization is not needed anymore because of React forget, currently known as React compiler. This April, our timeline finally caught up with theirs. React team released the compiler to the public and of course I had to try it and see the future for myself. So I tried the compiler on a few synthetic examples, I ran it on a few real apps, measured how it performs and what it does. Of course, I wrote it down and now I am happy to share with you how the future really looks like. So this is what the talk is all about.

2. Problem and Solution

Short description:

The problem the compiler solves is the performance impact of cascading re-renders in React. One way to address this is through memoization, which can be achieved using the React memo and hooks like useMemo and useCallback. By preserving references to non-primitive values between re-renders, we can prevent unnecessary re-renders and improve performance.

What is the problem the compiler solves? Are there any downsides to it? How it performs on synthetic examples and how it performs on real life code?

Let's start with the problem. So what exactly are we trying to solve here? Here is our beautiful user interface, it's really nice. When some new information comes in there, we want to update it. To do this in React, we trigger what is known as a re-render. Re-renders in React are cascading, as you probably know. Every time a re-render of a component is triggered, it triggers a re-render of every component inside and then every component inside this component until the end of the tree is reached. If those downstream re-renders affect some really heavy component, our app becomes slow. So that might cause performance problems.

To fix this, we need to stop this chain of re-renders from happening. One way to do it in React is to tell this component that it doesn't change and it can skip re-renders and re-render of every component inside. And of course, as always in React, there are multiple ways to do it, but one of them is memoization. Memoization starts with the React memo, a file or the component given to us by the React team. It wraps our original component and then renders itself on its place. Now, when the React reaches this component in the tree, it will stop and check whether its props have changed. If none of the props changed, then re-renders will be stopped. If even one of the props changes, React will continue with the re-renders as if no memoization happened. That means that for the memo to work properly, we need to make sure that every single prop on this component is exactly the same between the re-renders, otherwise, it just will not work.

For primitive values, it's easy. We don't need to do anything other than not changing them. For objects, arrays, and functions, however, they need some help. React uses referential equality to check for anything between re-renders. And if we declare those non-primitive values inside the component like I did here, they will be recreated on every re-render. Reference to them will change and memoization won't work. To fix this, we have two hooks, useMemo and useCallback. We will drop arrays and objects into useMemo, functions into useCallback, and then those hooks will preserve a reference to the values between the re-renders. And next time a re-render here in the parent happens, the very slow component will not re-render. And the chain of re-renders will be stopped. That is enough of the theory for today, I promise. This is a very simplified explanation, but as you can see, it's actually already quite complicated.

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