⚡ Bolt: Optimize BackToTop scroll event listener#109
Conversation
Throttled the scroll event listener in `BackToTop` using `requestAnimationFrame` to prevent main-thread blocking and excessive React re-renders. Also added `{ passive: true }` to the event listener to allow the browser to scroll smoothly.
Expected impact: Significant reduction in CPU usage and jank during fast scrolling.
Co-authored-by: anyulled <100741+anyulled@users.noreply.github.com>
|
The latest updates on your projects. Learn more about Vercel for GitHub.
|
|
👋 Jules, reporting for duty! I'm here to lend a hand with this pull request. When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down. I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job! For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with New to Jules? Learn more at jules.google/docs. For security, I will only act on instructions from the user who triggered this task. |
Review Summary by QodoOptimize BackToTop scroll event listener with throttling
WalkthroughsDescription• Throttles scroll events using requestAnimationFrame to prevent main-thread blocking • Adds passive event listener flag for smoother browser scrolling • Reduces excessive React re-renders during fast scrolling • Cancels pending animation frames on component unmount Diagramflowchart LR
A["Scroll Event"] -->|"requestAnimationFrame throttle"| B["State Update Batched"]
C["Passive Listener"] -->|"allows browser optimization"| D["Smooth Scrolling"]
B --> E["Reduced CPU Usage"]
D --> E
F["Cleanup"] -->|"cancelAnimationFrame"| G["Memory Leak Prevention"]
File Changes1. components/elements/BackToTop.tsx
|
Summary of ChangesHello, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed! This pull request significantly improves the performance and user experience of the "Back to Top" component by optimizing its scroll event handling. The changes aim to reduce CPU usage and eliminate potential UI jank during rapid scrolling, ensuring a smoother interaction for users. Highlights
Using Gemini Code AssistThe full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips. Invoking Gemini You can request assistance from Gemini at any point by creating a comment using either
Customization To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a Limitations & Feedback Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for GitHub and other Google products, sign up here. Footnotes
|
Code Review by Qodo
1. Redundant optimization block comment
|
|
No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Organization UI Review profile: CHILL Plan: Pro Run ID: 📒 Files selected for processing (1)
✅ Files skipped from review due to trivial changes (1)
📝 WalkthroughWalkthroughScroll handling in Changes
Estimated code review effort🎯 3 (Moderate) | ⏱️ ~20 minutes Poem
🚥 Pre-merge checks | ✅ 2 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (2 passed)
✏️ Tip: You can configure your own custom pre-merge checks in the settings. ✨ Finishing Touches🧪 Generate unit tests (beta)
📝 Coding Plan
Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out. Comment |
![gemini-code-assist[bot]](https://avatars.githubusercontent.com/in/956858?s=60&v=4){kind=small}
There was a problem hiding this comment.
Code Review
This pull request effectively optimizes the scroll event listener in the BackToTop component by using requestAnimationFrame to throttle state updates and adding { passive: true } to the event listener. This is a great performance improvement that will prevent scrolling jank. I've added one suggestion to further enhance the code's readability and maintainability by extracting a magic number and using more descriptive variable names.
| const state = { isTicking: false, tickingId: 0 }; | ||
|
|
||
| const onScroll = () => { | ||
| setHasScrolled(window.scrollY > 100); | ||
| if (!state.isTicking) { | ||
| state.tickingId = window.requestAnimationFrame(() => { | ||
| setHasScrolled(window.scrollY > 100); | ||
| state.isTicking = false; | ||
| }); | ||
| state.isTicking = true; | ||
| } | ||
| }; | ||
|
|
||
| window.addEventListener("scroll", onScroll); | ||
| return () => window.removeEventListener("scroll", onScroll); | ||
| window.addEventListener("scroll", onScroll, { passive: true }); | ||
| return () => { | ||
| window.removeEventListener("scroll", onScroll); | ||
| window.cancelAnimationFrame(state.tickingId); | ||
| }; |
There was a problem hiding this comment.
For improved readability and maintainability, I suggest a few refinements:
- Extract Magic Number: The scroll threshold
100is a magic number. Extracting it into a named constant likeSCROLL_THRESHOLD_PXmakes its purpose clear and simplifies future modifications. - Descriptive Naming: Renaming
statetothrottleStateandtickingIdtoanimationFrameIdmore accurately describes their roles within the throttling logic.
These changes make the implementation easier to understand at a glance.
const SCROLL_THRESHOLD_PX = 100;
const throttleState = { isTicking: false, animationFrameId: 0 };
const onScroll = () => {
if (!throttleState.isTicking) {
throttleState.animationFrameId = window.requestAnimationFrame(() => {
setHasScrolled(window.scrollY > SCROLL_THRESHOLD_PX);
throttleState.isTicking = false;
});
throttleState.isTicking = true;
}
};
window.addEventListener("scroll", onScroll, { passive: true });
return () => {
window.removeEventListener("scroll", onScroll);
window.cancelAnimationFrame(throttleState.animationFrameId);
};
![coderabbitai[bot]](https://avatars.githubusercontent.com/in/347564?s=60&v=4){kind=small}
There was a problem hiding this comment.
🧹 Nitpick comments (1)
components/elements/BackToTop.tsx (1)
8-13: Tighten the optimization comment to focus on rationale only.The block currently mixes “what it does” with “why.” Prefer a shorter why-focused note to match the repo’s self-documenting rule.
Proposed edit
- /* - * ⚡ Bolt Optimization: - * - Throttles scroll events using requestAnimationFrame to prevent main-thread blocking and excessive re-renders. - * - Uses passive event listener to allow the browser to perform smooth scrolling without waiting for JS execution. - * Expected impact: Significant reduction in CPU usage and jank during fast scrolling. - */ + /* + * Use rAF + passive scroll listener to reduce scroll-thread contention and avoid + * unnecessary work during rapid scrolling. + */As per coding guidelines, "Code must be self-documenting. Only explain why non-obvious decisions were made in comments. DO NOT add inline comments explaining what code does."
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed. In `@components/elements/BackToTop.tsx` around lines 8 - 13, Update the comment block in BackToTop.tsx (near the BackToTop component/scroll handler) to remove the "what it does" lines and keep a single-line rationale explaining why the optimization exists (e.g., to reduce CPU usage and jank during fast scrolling); replace the multi-bullet description about throttling and passive listeners with a concise why-focused note that the requestAnimationFrame/passive listener approach reduces main-thread work and improves scroll smoothness.
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Nitpick comments:
In `@components/elements/BackToTop.tsx`:
- Around line 8-13: Update the comment block in BackToTop.tsx (near the
BackToTop component/scroll handler) to remove the "what it does" lines and keep
a single-line rationale explaining why the optimization exists (e.g., to reduce
CPU usage and jank during fast scrolling); replace the multi-bullet description
about throttling and passive listeners with a concise why-focused note that the
requestAnimationFrame/passive listener approach reduces main-thread work and
improves scroll smoothness.
ℹ️ Review info
⚙️ Run configuration
Configuration used: Organization UI
Review profile: CHILL
Plan: Pro
Run ID: 3fa11dec-0dbe-467e-8459-df780a7cc832
📒 Files selected for processing (1)
components/elements/BackToTop.tsx
Ran `npm run format` to automatically apply prettier formatting across the codebase to fix CI format check failures. Co-authored-by: anyulled <100741+anyulled@users.noreply.github.com>
1 participant
💡 What: Wrapped the
onScrollcallback incomponents/elements/BackToTop.tsxwith a throttle usingrequestAnimationFrameand added{ passive: true }to the scroll event listener.🎯 Why: The previous implementation triggered a React state update (
setHasScrolled) on every single scroll event tick synchronously, which can block the main thread and cause scrolling jank.📊 Impact: Significantly reduces CPU usage and eliminates potential jank during fast scrolling by batching state updates to the browser's render cycle and allowing the browser to optimize scrolling.
🔬 Measurement:
onScrollfunction calls and React render cycles in the Main thread flame chart compared to the unoptimized version.PR created automatically by Jules for task 4421907313861527540 started by @anyulled
Summary by CodeRabbit