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⚡ Bolt: Optimize scroll event listeners with requestAnimationFrame and passive flag #118

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⚡ Bolt: Optimize scroll event listeners with requestAnimationFrame an…
anyulled Mar 24, 2026
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⚡ Bolt: Optimize scroll event listeners with requestAnimationFrame an…
anyulled Mar 24, 2026
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21 changes: 3 additions & 18 deletions .jules/bolt.md
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Original file line number Diff line number Diff line change
@@ -1,19 +1,4 @@
## 2026-02-01 - Hidden CSS Images
## 2026-03-24 - Optimizing Scroll Event Listeners with requestAnimationFrame

**Learning:** Found critical hero images being loaded via CSS `background-image` in React components, bypassing Next.js image optimization.
**Action:** grep for `style={{.*backgroundImage.*url` or `url(` in components to find hidden unoptimized images.

## 2026-02-01 - Package Lock Noise

**Learning:** `package-lock.json` generated massive diffs (removing dev dependencies like `webpack`) during `npm install`. This indicates environment mismatch.
**Action:** When working on small optimizations, always verify `package-lock.json` diffs and revert them if they include unrelated changes, to avoid breaking the build.

## 2026-02-01 - Client-Side Fetching Anti-Pattern in App Router

**Learning:** Found `useEffect` fetching static content (Speakers) in a Client Component (`Section5`) on the homepage. This caused unnecessary layout shifts and delayed LCP.
**Action:** Move data fetching to the parent Server Component (`page.tsx`) and pass data as props. This leverages ISR caching and eliminates client-side waterfall.

## 2026-03-18 - Immutability constraints over performance in grouping loops

**Learning:** When attempting to optimize an O(N^2) array spread operation (`[...existing, talk]`) inside a grouping loop in `groupTalksByTrack`, the purely functional/immutable constraint specified by the team (and the lack of `Map.groupBy` support in Node 20.x Jest environments) means that we must fall back to immutable reductions.
**Action:** When constraints require strict immutability without mutation of objects, use `reduce` with object and array spreads (e.g., `{ ...acc, [key]: [...(acc[key] || []), item] }`) even if it introduces O(N^2) overhead for large arrays. Avoid using `push()` or modifying accumulators directly. Always run Prettier/formatting checks before merge to resolve CI failures.
**Learning:** Global scroll event listeners without throttling or `{ passive: true }` block the browser's main thread on every scroll tick, causing jank and layout shifts in performance-critical areas. Using `requestAnimationFrame` to throttle state updates significantly improves scrolling performance by syncing state updates with the browser's paint cycle.
**Action:** When adding `addEventListener('scroll', ...)` in React components, ensure the event is throttled using `requestAnimationFrame`. To track the ticking state while bypassing `no-restricted-syntax` (no `let` variables), wrap the state in a constant object (`const state = { isTicking: false };`) and mutate its properties. Always provide ` { passive: true }` to the listener. In Jest tests simulating scroll, mock `requestAnimationFrame` to synchronously execute the callback (`window.requestAnimationFrame = (cb) => { cb(0); return 0; }`).
11 changes: 11 additions & 0 deletions __tests__/components/layout/DynamicHeaderWrapper.test.tsx
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Expand Up @@ -52,8 +52,19 @@ describe("DynamicHeaderWrapper", () => {
expect(screen.getByTestId("header8")).toHaveAttribute("data-scroll", "false");

Object.defineProperty(window, "scrollY", { value: 120, writable: true, configurable: true });

// Mock requestAnimationFrame
const originalRAF = window.requestAnimationFrame;
window.requestAnimationFrame = (callback) => {
callback(0);
return 0;
};

fireEvent.scroll(document);

expect(screen.getByTestId("header8")).toHaveAttribute("data-scroll", "true");

// Restore original requestAnimationFrame
window.requestAnimationFrame = originalRAF;
});
});
11 changes: 11 additions & 0 deletions __tests__/components/layout/Layout.test.tsx
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Expand Up @@ -96,8 +96,19 @@ describe("Layout", () => {
expect(screen.getByTestId("header-1")).toHaveAttribute("data-scroll", "false");

Object.defineProperty(window, "scrollY", { value: 150, writable: true, configurable: true });

// Mock requestAnimationFrame
const originalRAF = window.requestAnimationFrame;
window.requestAnimationFrame = (callback) => {
callback(0);
return 0;
};
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@qodo-code-review qodo-code-review Bot Mar 24, 2026

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Action required

3. Test raf mock breaks strict ts 🐞 Bug ✓ Correctness

The new test overrides window.requestAnimationFrame with a function whose callback parameter is
implicitly any, which fails TypeScript strict mode when running npm run type-check.
This can block CI even if Jest tests pass.
Agent Prompt 
### Issue description
TypeScript strict mode rejects the test rAF mock because the `callback` parameter is implicitly `any`.

### Issue Context
`tsconfig.json` is `strict: true` and includes all `**/*.ts(x)` files, including tests.

### Fix Focus Areas
- __tests__/components/layout/Layout.test.tsx[100-105]
- __tests__/components/layout/DynamicHeaderWrapper.test.tsx[56-61]
- tsconfig.json[1-28]

### Implementation notes
- Type the mock as `const rafMock: typeof window.requestAnimationFrame = (cb: FrameRequestCallback) => { cb(0); return 0; };`.
- Prefer `try/finally` to restore the original RAF even if an assertion throws.

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools


fireEvent.scroll(document);

expect(screen.getByTestId("header-1")).toHaveAttribute("data-scroll", "true");

// Restore original requestAnimationFrame
window.requestAnimationFrame = originalRAF;
});
});
12 changes: 6 additions & 6 deletions __tests__/snapshots/layout/__snapshots__/Footer8.test.tsx.snap
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Expand Up @@ -11,8 +11,8 @@ exports[`Footer8 Component matches snapshot 1`] = `
decoding="async"
loading="lazy"
sizes="100vw"
src="/_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=3840&q=75"
srcset="/_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=640&q=75 640w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=750&q=75 750w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=828&q=75 828w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=1080&q=75 1080w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=1200&q=75 1200w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=1920&q=75 1920w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=2048&q=75 2048w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=3840&q=75 3840w"
src="/_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=3840&q=85"
srcset="/_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=640&q=85 640w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=750&q=85 750w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=828&q=85 828w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=1080&q=85 1080w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=1200&q=85 1200w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=1920&q=85 1920w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=2048&q=85 2048w, /_next/image?url=%2Fassets%2Fimg%2Fbg%2Fheader-bg21.png&w=3840&q=85 3840w"
style="position: absolute; height: 100%; width: 100%; left: 0px; top: 0px; right: 0px; bottom: 0px; object-fit: cover; color: transparent; z-index: -3;"
/>
<img
Expand All @@ -22,8 +22,8 @@ exports[`Footer8 Component matches snapshot 1`] = `
decoding="async"
height="230"
loading="lazy"
src="/_next/image?url=%2Fassets%2Fimg%2Felements%2Flayer1.png&w=3840&q=75"
srcset="/_next/image?url=%2Fassets%2Fimg%2Felements%2Flayer1.png&w=1920&q=75 1x, /_next/image?url=%2Fassets%2Fimg%2Felements%2Flayer1.png&w=3840&q=75 2x"
src="/_next/image?url=%2Fassets%2Fimg%2Felements%2Flayer1.png&w=3840&q=85"
srcset="/_next/image?url=%2Fassets%2Fimg%2Felements%2Flayer1.png&w=1920&q=85 1x, /_next/image?url=%2Fassets%2Fimg%2Felements%2Flayer1.png&w=3840&q=85 2x"
style="color: transparent;"
width="1440"
/>
Expand All @@ -45,8 +45,8 @@ exports[`Footer8 Component matches snapshot 1`] = `
decoding="async"
height="76"
loading="lazy"
src="/_next/image?url=%2Fassets%2Fimg%2Flogo%2FdevBcn.webp&w=384&q=75"
srcset="/_next/image?url=%2Fassets%2Fimg%2Flogo%2FdevBcn.webp&w=256&q=75 1x, /_next/image?url=%2Fassets%2Fimg%2Flogo%2FdevBcn.webp&w=384&q=75 2x"
src="/_next/image?url=%2Fassets%2Fimg%2Flogo%2FdevBcn.webp&w=384&q=85"
srcset="/_next/image?url=%2Fassets%2Fimg%2Flogo%2FdevBcn.webp&w=256&q=85 1x, /_next/image?url=%2Fassets%2Fimg%2Flogo%2FdevBcn.webp&w=384&q=85 2x"
style="color: transparent;"
width="150"
/>
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