The Art of Ignoring Best Practices for React Performance

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Have you ever wanted to break the rules and be a React troublemaker? I’ll show you how ignoring React’s best practices can improve performance, all without major rewrites to your codebase. To understand how, we’ll learn when React decides to render and how to trick it to render less frequently. We’ll build components that don’t render anything, conditionally call hooks, and even use a piece of Svelte - all to quickly fix real performance problems I encountered at Microsoft.

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

FAQ

The speaker is Tigerhooks, a senior software engineer at Microsoft who has worked on web browsers like Edge, Chrome, and Firefox.

The main topic is about breaking React best practices to improve performance, including techniques like conditionally calling hooks, using impure components, and incorporating a second UI library.

React rerenders components mainly due to state changes. When a state update occurs, the component and all its descendants rerender to keep the UI in sync with the state.

React.Memo is a higher-order component that prevents rerenders if the component's props haven't changed. It helps optimize performance by memoizing the component's output.

You can use React DevTools Profiler to track component rerenders. It has settings like 'Highlight Updates When Components Re-render' and 'Record Why Each Component Rendered While Profiling' to help identify rerenders.

The ExpensiveEffect component isolates state changes by running side effects and not rendering any children. This helps in preventing unnecessary rerenders of the entire component tree.

You can use Svelte's store API to manage state without affecting React's component tree. This allows you to update state and notify components without causing unnecessary rerenders.

Svelte stores provide a set method to update state and notify components watching the store. This reduces the need for React's useState and helps in preventing excessive rerenders.

Redux uses a static store reference passed through React context, updating only the necessary components. In contrast, the useReducer hook can cause the entire tree to rerender when any state changes.

Svelte stores know how many listeners are attached and can clean up based on listener presence. This helps in efficiently managing resources and avoiding memory leaks.

Tiger Oakes
Tiger Oakes
19 min
18 Jun, 2024

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Video Summary and Transcription

This Talk introduces the concept of being a 'React bad boy' by ignoring best practices and optimizing React rendering. It explains how to avoid unnecessary rerenders using React.memo and React DevTools. It also covers advanced techniques like isolating state changes and lazy loading hooks. The Talk explores reducing component rerenders using Svelte stores and optimizing with swap stores in Redux. These techniques improve React performance without the need for major refactors or rewrites.

1. Introduction to React Bad Boy

Short description:

Have you ever wanted to be a React bad boy? I'm going to show you the art of ignoring best practices. We'll talk about when does React decide to rerender, then how to isolate expensive hooks and state changes using impure components, and how to only update leaf components by using a different UI library.

Have you ever wanted to be a React bad boy? I know you've all been good engineers following all the best practices, but where has that gotten you? Into complex React projects with slow components? Then you find yourself wanting to smash your mechanical keyboard, wondering why you need to use unidirectional data flow to avoid calling React hooks conditionally, to store state using React's useState hook. You hear a little voice whispering, you can be a React troublemaker. You can break all of these rules. You think jaywalking, littering, and riding a motorcycle is bad. Wait until you conditionally call React hooks, build impure components, and even pull in a second UI library?

My name is tigerhooks. You can find me at notwoods and all the socials. I'm a senior software engineer working at Microsoft and I previously helped build three web browsers, Edge, Chrome, and Firefox. I've worked with React for over eight years, and I am going to show you the art of ignoring best practices. Any documentation you read comes with a hidden asterisk. It covers most cases, but we all have different setups and environments. This talk will show you the edge cases that you know when to follow and when not to follow best practices and how to get yourself on Santa's Nautilus this Christmas. Since we're in dangerous territory, use what I'm about to show you with caution. Some of these tricks can make your code hard to follow. Use your best judgment, evaluate tradeoffs, and communicate what you're trying to do. Here is what I'll show you today. We'll talk about when does React decide to rerender, then how to isolate expensive hooks and state changes using impure components, and how to only update leaf components by using a different UI library.

Let's start with the first topic. When does React rerender? Well, React starts with a simple rule. Every rerender starts with a state change. You might be thinking, wait, don't components rerender when their props change? When context changes? But no, the trick is that whenever a component rerenders, it also rerenders every descendant component. React uses rerenders to figure out what needs to change to keep your UI in sync with state. Your component will return a mix of other components and HTML elements. When another component is encountered, React will then proceed to render it, and that component will return another mix of components and HTML elements. Eventually, React will just be left with an HTML tree. Now that it's finished rerendering components, it will begin the process of virtual DOM diffing. React will compare the new HTML against the previously rendered HTML, and then update the nodes that have changed in the DOM. But React does not think too hard about what components to render. You might think that only components that read the state will update, but actually everything rerenders. It doesn't matter if the state is passed in as a prop, or if the component takes no props at all. Whenever this increment button is clicked, and the counter state is updated, the MyCounter component and all its descendants will re-render as indicated by these green flashes.

2. Avoiding Unnecessary Rerenders

Short description:

Even though the title component doesn't read the count state, it also re-renders. React.Memo can help reduce unnecessary re-renders. React DevTools can highlight re-rendered components and track down the cause. Check out Josh Komu's article for more details.

Even though the title component doesn't read the count state, it also re-renders. The only exception to this is React.Memo. Memo places an extra layer around a component, which tells React, if my props are the same, I pinky promise that I would return the exact same result. You can just remember what I returned last time. No need to render me again. Now whenever this increment button is clicked, and the counter state is updated, MyCounter will re-render, and then it will attempt to re-render its descendants. Title doesn't read the count state, so its props have not changed. As a result, it doesn't re-render, thanks to React.Memo. MyCounter display is still re-rendered, as this count prop is changing. Now Memo is a little bit weird with React.Context. Context acts like a second set of invisible props, past every component. So if your component is using React.Memo, the props and context it's reading must be exactly the same, or else the component will be caused to re-render. If you want to see whenever a component re-renders in your own code, React DevTools can help out. After opening your browser's developer tools, you can go to React's Profiler tab, click on the gear icon to open the extension settings, and then turn on a setting labeled, Highlight Updates When Components Re-render. This will cause green rectangles to flash around each re-rendered component in your UI. And if you're trying to track down what's causing a re-render in your code, you can turn on a different setting labeled, Record Why Each Component Rendered While Profiling. You can find it under the Profiler tab in React's DevTools settings dialog. Then, when you save a recording using React's Profiler, each render will be captured and you can see what triggered it. If you want to learn more, you can check out Josh Komu's excellent article with live samples you can play with.

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