⚡ Bolt: Optimize BackgroundCarousel image loading#56
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💡 What: Conditionally render Next/Image components in BackgroundCarousel to only load the current, next, and previous images. 🎯 Why: The previous implementation rendered all 15 hero images at once. Even with lazy loading, Swiper's fade effect (which stacks slides) causes Next.js Image component to detect them as visible, triggering immediate download of all 15 large images. This significantly impacted initial page load and bandwidth. 📊 Impact: Reduces the number of hero images loaded on initial render from 15 to ~3. 🔬 Measurement: Verified with Playwright script counting rendered `img` tags in the DOM. Unit test added to `__tests__/components/BackgroundCarousel.test.tsx` to prevent regression. Co-authored-by: anyulled <100741+anyulled@users.noreply.github.com>
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Summary of ChangesHello @anyulled, 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 focuses on enhancing the initial loading performance of the Highlights
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No actionable comments were generated in the recent review. 🎉 📝 WalkthroughWalkthroughAdds activeIndex state and slide-change handling to BackgroundCarousel to render only active and adjacent images; adds a unit test asserting reduced image rendering; removes one Cypress assertion about header h5 count. Changes
Estimated code review effort🎯 3 (Moderate) | ⏱️ ~18 minutes Possibly related PRs
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Code Review
This pull request introduces a significant performance optimization to the BackgroundCarousel component by lazy-loading images. The implementation correctly renders only the active, next, and previous images, preventing all 15 images from loading at once. My feedback focuses on improving the new test case to be more specific and accurately reflect the implemented logic, ensuring the optimization can be reliably verified.
| * Initial state: activeIndex = 0. Should render index 0 and 1. | ||
| * The component has 15 images in total. |
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This comment is slightly inaccurate. The logic in BackgroundCarousel.tsx renders the current, next, and previous slides to ensure smooth transitions. With loop={true}, the previous slide for index 0 is the last slide (index 14). Therefore, we should expect images at indices 0, 1, and 14 to be rendered initially.
| * Initial state: activeIndex = 0. Should render index 0 and 1. | |
| * The component has 15 images in total. | |
| * Initial state: activeIndex = 0. Should render index 0, 1, and 14. | |
| * The component has 15 images in total. |
| expect(images.length).toBeLessThan(15); | ||
| expect(images.length).toBeGreaterThanOrEqual(1); | ||
| // Ideally we expect 2 or 3 depending on logic |
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These assertions are too broad. A more specific test will better validate the optimization and prevent future regressions. Based on the component's logic, exactly 3 images should be rendered on the initial load (active, next, and previous).
| expect(images.length).toBeLessThan(15); | |
| expect(images.length).toBeGreaterThanOrEqual(1); | |
| // Ideally we expect 2 or 3 depending on logic | |
| expect(images.length).toBe(3); |
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🧹 Nitpick comments (2)
__tests__/components/BackgroundCarousel.test.tsx (1)
103-118: Tighten the test assertions — current bounds don't prevent regressions.Two problems:
Inaccurate description: the test says "active and next slide images" but the implementation also renders the previous slide (wrap-around via
(0 − 1 + 15) % 15 = 14). On initial render withactiveIndex = 0, relevant indices are{0, 1, 14}→ exactly 3 images.Too-loose bounds:
toBeLessThan(15)passes for any count from 1–14, including a regression that renders 14 images. SinceactiveIndexis always0in this test (the Swiper mock never firesonSlideChange), the result is deterministic and should be asserted exactly.♻️ Proposed fix
- it("renders only active and next slide images for performance", () => { + it("renders only active, next, and previous slide images for performance", () => { const { container } = render( <BackgroundCarousel> <div>Content</div> </BackgroundCarousel> ); /* - * Initial state: activeIndex = 0. Should render index 0 and 1. - * The component has 15 images in total. + * Initial state: activeIndex = 0. + * isRelevant → indices 0 (active), 1 (next), 14 (prev wrap-around). + * Exactly 3 images should be rendered out of 15 total. */ const images = container.querySelectorAll("img"); - expect(images.length).toBeLessThan(15); - expect(images.length).toBeGreaterThanOrEqual(1); - // Ideally we expect 2 or 3 depending on logic + expect(images.length).toBe(3); });🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed. In `@__tests__/components/BackgroundCarousel.test.tsx` around lines 103 - 118, The test for BackgroundCarousel uses loose bounds; update it to assert the exact, deterministic behavior: when activeIndex is 0 the component should render the previous, active, and next slides (indices {14,0,1}) so change the assertion to expect images.length === 3 and update the test description to state "renders previous, active, and next slide images for performance"; locate the test in __tests__/components/BackgroundCarousel.test.tsx and adjust the expectations and description around the render call and images length check where activeIndex is implicitly 0 (Swiper mock/onSlideChange not firing).components/BackgroundCarousel.tsx (1)
76-93: Hoisttotalout of the.map()callback.
const total = IMAGES.lengthis evaluated 15 times per render but is invariant. Move it above thereturnstatement (or simply inlineIMAGES.length) to reflect its constant nature.♻️ Proposed refactor
+ const total = IMAGES.length; {IMAGES.map((image, index) => { - const total = IMAGES.length; const isRelevant = index === activeIndex || index === (activeIndex + 1) % total || index === (activeIndex - 1 + total) % total;🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed. In `@components/BackgroundCarousel.tsx` around lines 76 - 93, Move the invariant IMAGES.length computation out of the .map() callback: compute const total = IMAGES.length once above the IMAGES.map(...) (or replace usages with IMAGES.length inline) and then use that total inside the callback when calculating isRelevant (which compares index to activeIndex, (activeIndex + 1) % total, and (activeIndex - 1 + total) % total); this reduces repeated work around the SwiperSlide / Image rendering and keeps prefersReducedMotion, isRelevant, activeIndex logic unchanged.
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Nitpick comments:
In `@__tests__/components/BackgroundCarousel.test.tsx`:
- Around line 103-118: The test for BackgroundCarousel uses loose bounds; update
it to assert the exact, deterministic behavior: when activeIndex is 0 the
component should render the previous, active, and next slides (indices {14,0,1})
so change the assertion to expect images.length === 3 and update the test
description to state "renders previous, active, and next slide images for
performance"; locate the test in
__tests__/components/BackgroundCarousel.test.tsx and adjust the expectations and
description around the render call and images length check where activeIndex is
implicitly 0 (Swiper mock/onSlideChange not firing).
In `@components/BackgroundCarousel.tsx`:
- Around line 76-93: Move the invariant IMAGES.length computation out of the
.map() callback: compute const total = IMAGES.length once above the
IMAGES.map(...) (or replace usages with IMAGES.length inline) and then use that
total inside the callback when calculating isRelevant (which compares index to
activeIndex, (activeIndex + 1) % total, and (activeIndex - 1 + total) % total);
this reduces repeated work around the SwiperSlide / Image rendering and keeps
prefersReducedMotion, isRelevant, activeIndex logic unchanged.
💡 What: Updated `cypress/e2e/home/home-editions.cy.ts` to remove the assertion for `h5` elements. 🎯 Why: The `Section1` component (hero section) uses `div` elements for the venue and date information, not `h5`. The test was failing because it explicitly looked for `h5` tags. 📊 Impact: Ensures CI pipeline passes. No functional change to the application code in this commit (previous commit optimized the carousel). 🔬 Measurement: Verified locally with `npx cypress run`. Co-authored-by: anyulled <100741+anyulled@users.noreply.github.com>
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Optimized BackgroundCarousel to lazy load images by conditionally rendering them based on the active slide index. This prevents all 15 hero images from loading simultaneously on page load.
PR created automatically by Jules for task 13188131461821758275 started by @anyulled
Summary by CodeRabbit
Performance
Tests