Nadia Makarevich – How React Compiler Performs on Real Code, React Advanced 2024

Summary

In this talk, Nadia explores the React compiler, a tool that automates memoization to optimize performance by reducing unnecessary re-renders in React applications. She demonstrates its effectiveness with both synthetic and real-world examples, showing how it can improve interaction performance with minimal impact on initial load times. While the compiler offers significant performance gains for most applications, Nadia highlights its limitations, especially with complex data and external libraries. Ultimately, the compiler provides a 'good enough' optimization for most developers, but fine-tuning may still be required for performance-critical scenarios.

Takeaways

• 😀 **React Compiler Simplifies Memoization**: The new React compiler automates memoization, helping developers reduce unnecessary re-renders with minimal effort.
• 😀 **Performance Improvements**: The compiler can significantly improve performance by optimizing the rendering of components, even in complex cases with child components.
• 😀 **Testing with Synthetic Examples**: In synthetic tests, the compiler was able to optimize props and hooks automatically, reducing re-renders without any manual intervention.
• 😀 **Real-World Performance Testing**: In real-world scenarios, the compiler showed strong performance gains, particularly in reducing interaction times (e.g., switching between light and dark mode).
• 😀 **Not All Re-Renders Are Avoided**: While the compiler works well in many cases, some complex or non-standard patterns (like passing non-primitive values) may still result in unnecessary re-renders.
• 😀 **External Libraries Aren't Compiled**: The compiler doesn’t transpile third-party libraries, so developers still need to handle performance optimizations manually when using such libraries.
• 😀 **Manual Optimization Still Necessary for Performance-Critical Apps**: For applications that demand the highest performance, developers may still need to handle memoization manually to optimize for every millisecond.
• 😀 **Memorization Hooks**: React's manual memorization tools (like `React.memo`, `useMemo`, and `useCallback`) are still useful but are often handled by the compiler automatically.
• 😀 **Minimal Impact on Initial Load**: The compiler showed minimal impact on the initial loading performance of apps, meaning it doesn't slow down the app's first render significantly.
• 😀 **Ongoing Need for Deep Understanding**: Even with the compiler, developers still need to understand React’s rendering process to optimize performance in more complex cases or when working with legacy code.

Q & A

What is the main focus of the talk?

The main focus of the talk is on React's performance optimization, specifically how the React compiler addresses re-rendering issues and simplifies memoization in React applications.

What problem does the React compiler aim to solve?

The React compiler aims to solve the problem of excessive re-renders in React applications, which can degrade performance, particularly in large and complex UIs.

How does React's default rendering behavior cause performance issues?

React’s default behavior triggers cascading re-renders whenever a component’s state or props change. This can result in slow performance if these re-renders affect heavy components or if there are unnecessary updates in the component tree.

What is memoization in React, and how is it typically applied?

Memoization in React involves preventing unnecessary re-renders by checking if a component’s props have changed. Common techniques include `React.memo`, `useMemo`, and `useCallback` to optimize performance by skipping re-renders when the data hasn’t changed.

What makes the React compiler different from traditional memoization?

The React compiler is smarter than traditional memoization. Instead of blindly wrapping components in `memo`, it analyzes component code and automatically applies memoization where needed based on dependencies and prop changes.

How does the React compiler handle object and function references?

The React compiler automatically optimizes object and function references, ensuring they are memoized correctly. For instance, if a component’s prop is an object or function that doesn’t change, the compiler will preserve the reference across re-renders, reducing unnecessary updates.

What did the speaker find when testing the React compiler on synthetic examples?

The speaker found that the React compiler effectively optimized re-renders in synthetic examples. Components that should not re-render, such as slow ones or those with unchanged props, were successfully memoized, leading to improved performance in the test cases.

What were the results of applying the React compiler to a real app?

When applied to a real app, the React compiler showed a noticeable but varied impact on performance. It improved the initial load time slightly, and significantly enhanced interaction performance. However, some edge cases, particularly with external libraries, still required manual optimization.

Did the React compiler affect the initial load performance of the app?

The React compiler had a minimal impact on initial load performance. While some measurements showed slight improvements or declines, the overall effect was negligible, making it a good option for optimizing performance without negatively affecting the first load.

What was the most notable issue with the compiler during the real-world app testing?

The most notable issue was that the compiler could not optimize re-renders caused by non-primitive props or external libraries with complex behavior. For instance, issues arose when dealing with dynamic keys in React Query, which caused references to change unexpectedly.

Can developers completely forget about manual memoization if they use the React compiler?

No, developers cannot completely forget about manual memoization. While the React compiler automates much of the process, there are still edge cases where manual intervention is necessary, especially when dealing with external libraries or specific performance requirements.

What is the overall conclusion about using the React compiler for performance optimization?

The React compiler offers a significant performance boost for most developers by automatically handling memoization. For most use cases, enabling the compiler should provide sufficient performance gains with minimal overhead. However, developers with specific performance needs may still need to manually optimize certain aspects of their app.