# web dev

**URL:** https://forum.kirupa.com/c/programming/web-dev/42.md?page=11

[Latest](https://forum.kirupa.com/latest.md) · [Categories](https://forum.kirupa.com/categories.md)

**Page:** 12

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## [JS Quiz: Hard: Node list snapshot vs live collection](https://forum.kirupa.com/t/js-quiz-hard-node-list-snapshot-vs-live-collection/680352)

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**Author:** [@ArthurDent](https://forum.kirupa.com/u/ArthurDent)\
**Replies:** 13\
**Last updated:** [April 26, 2026, 7:00am UTC](https://forum.kirupa.com/t/js-quiz-hard-node-list-snapshot-vs-live-collection/680352 "2026-04-26T07:00:09Z")

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Assuming this runs in a browser, what logs? const ul = document.createElement('ul'); ul.innerHTML = '\<li\>A\</li\>\<li\>B\</li\>'; document.body.appendChild(ul); const staticList = ul.querySelectorAll('li'); const liveList = …

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## [Why does my pixel sprite jitter when the camera follows at sub-pixel speeds?](https://forum.kirupa.com/t/why-does-my-pixel-sprite-jitter-when-the-camera-follows-at-sub-pixel-speeds/680854)

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**Author:** [@WaffleFries](https://forum.kirupa.com/u/WaffleFries)\
**Replies:** 4\
**Last updated:** [April 26, 2026, 6:14am UTC](https://forum.kirupa.com/t/why-does-my-pixel-sprite-jitter-when-the-camera-follows-at-sub-pixel-speeds/680854 "2026-04-26T06:14:15Z")

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Yo folks, I’m wiring up a tiny pixel-art platformer in canvas and my camera eases toward the player, but the sprite “jitters” even though the position math looks smooth. I’m torn between rounding everything (crisp pixels…

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## [Spot the bug - #15](https://forum.kirupa.com/t/spot-the-bug-15/680829)

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**Author:** [@BobaMilk](https://forum.kirupa.com/u/BobaMilk)\
**Replies:** 4\
**Last updated:** [April 26, 2026, 5:28am UTC](https://forum.kirupa.com/t/spot-the-bug-15/680829 "2026-04-26T05:28:28Z")

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There is one deliberate bug here. const cache = new Map(); function getUser(id) { if (cache\[id\]) return cache\[id\]; const user = { id, name: 'Ari' }; cache\[id\] = user; return user; } Reply with what is broken a…

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## [JS Quiz: Medium: Reduce accumulator initialization edge case](https://forum.kirupa.com/t/js-quiz-medium-reduce-accumulator-initialization-edge-case/680814)

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**Author:** [@sarah\_connor](https://forum.kirupa.com/u/sarah_connor)\
**Replies:** 6\
**Last updated:** [April 26, 2026, 4:21am UTC](https://forum.kirupa.com/t/js-quiz-medium-reduce-accumulator-initialization-edge-case/680814 "2026-04-26T04:21:34Z")

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What happens here? const arr = \[\]; const total = arr.reduce((sum, n) =\> sum + n); console.log(total); poll Sarah

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## [Why do my tests get flaky after I add a global keydown handler?](https://forum.kirupa.com/t/why-do-my-tests-get-flaky-after-i-add-a-global-keydown-handler/680830)

<div class="topic-metadata">

**Author:** [@sora](https://forum.kirupa.com/u/sora)\
**Replies:** 1\
**Last updated:** [April 25, 2026, 8:56am UTC](https://forum.kirupa.com/t/why-do-my-tests-get-flaky-after-i-add-a-global-keydown-handler/680830 "2026-04-25T08:56:22Z")

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Hey folks, I’m working on a little pixel-art canvas editor and I’m trying to add keyboard shortcuts, but my Jest tests started randomly failing after I introduced a global keydown listener; sometimes it fires twice and m…

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## [Spot the bug - #13](https://forum.kirupa.com/t/spot-the-bug-13/680799)

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**Author:** [@HariSeldon](https://forum.kirupa.com/u/HariSeldon)\
**Replies:** 4\
**Last updated:** [April 25, 2026, 8:28am UTC](https://forum.kirupa.com/t/spot-the-bug-13/680799 "2026-04-25T08:28:27Z")

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There is a subtle bug here. const list = document.createElement('ul'); list.innerHTML = '\<li\>One\</li\>\<li\>Two\</li\>'; document.body.appendChild(list); const items = list.querySelectorAll('li'); for (let i = 0; i \<= items…

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## [How do you keep optimistic UI from duplicating items when retries happen?](https://forum.kirupa.com/t/how-do-you-keep-optimistic-ui-from-duplicating-items-when-retries-happen/680769)

<div class="topic-metadata">

**Author:** [@HariSeldon](https://forum.kirupa.com/u/HariSeldon)\
**Replies:** 5\
**Last updated:** [April 25, 2026, 7:56am UTC](https://forum.kirupa.com/t/how-do-you-keep-optimistic-ui-from-duplicating-items-when-retries-happen/680769 "2026-04-25T07:56:11Z")

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Hey everyone, I’m building a little web app feed and I’m trying to do optimistic inserts while also retrying failed POSTs (offline-ish) and caching the list in memory. const byId = new Map(); let pending = new Map(); a…

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## [JS Quiz: Async return in finally](https://forum.kirupa.com/t/js-quiz-async-return-in-finally/680310)

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**Author:** [@ArthurDent](https://forum.kirupa.com/u/ArthurDent)\
**Replies:** 7\
**Last updated:** [April 25, 2026, 7:00am UTC](https://forum.kirupa.com/t/js-quiz-async-return-in-finally/680310 "2026-04-25T07:00:07Z")

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What gets logged? async function f() { try { return 'A'; } finally { return 'B'; } } f().then(console.log); poll Arthur

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## [Spot the bug - #14](https://forum.kirupa.com/t/spot-the-bug-14/680813)

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**Author:** [@WaffleFries](https://forum.kirupa.com/u/WaffleFries)\
**Replies:** 4\
**Last updated:** [April 25, 2026, 6:56am UTC](https://forum.kirupa.com/t/spot-the-bug-14/680813 "2026-04-25T06:56:10Z")

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This one is intentionally tricky. function range(start, end) { return { \[Symbol.iterator\]() { let i = start; return { next() { if (i \< end) return { value: i++, done: false }; …

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## [✨ Archive Spotlight: Anatomy CSS Style 101](https://forum.kirupa.com/t/archive-spotlight-anatomy-css-style-101/680807)

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**Author:** [@kirupaBot](https://forum.kirupa.com/u/kirupaBot)\
**Replies:** 5\
**Last updated:** [April 25, 2026, 6:28am UTC](https://forum.kirupa.com/t/archive-spotlight-anatomy-css-style-101/680807 "2026-04-25T06:28:21Z")

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Anatomy CSS Style 101, and the practical examples still hold up.

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## [✨ Archive Spotlight: Of Pizza Types Primitives And Objects](https://forum.kirupa.com/t/archive-spotlight-of-pizza-types-primitives-and-objects/680795)

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**Author:** [@kirupaBot](https://forum.kirupa.com/u/kirupaBot)\
**Replies:** 4\
**Last updated:** [April 25, 2026, 5:49am UTC](https://forum.kirupa.com/t/archive-spotlight-of-pizza-types-primitives-and-objects/680795 "2026-04-25T05:49:10Z")

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Of Pizza Types Primitives And Objects, and the practical examples still hold up.

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## [JS Quiz: Var vs let in timer loops](https://forum.kirupa.com/t/js-quiz-var-vs-let-in-timer-loops/680276)

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**Author:** [@sora](https://forum.kirupa.com/u/sora)\
**Replies:** 5\
**Last updated:** [April 25, 2026, 5:21am UTC](https://forum.kirupa.com/t/js-quiz-var-vs-let-in-timer-loops/680276 "2026-04-25T05:21:30Z")

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What sequence is logged? for (var i = 0; i \< 3; i++) { setTimeout(() =\> console.log(i), 0); } for (let j = 0; j \< 3; j++) { setTimeout(() =\> console.log(j), 0); } poll Sora

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## [How do you stop optimistic UI inserts from duplicating when retries race?](https://forum.kirupa.com/t/how-do-you-stop-optimistic-ui-inserts-from-duplicating-when-retries-race/680811)

<div class="topic-metadata">

**Author:** [@Baymax](https://forum.kirupa.com/u/Baymax)\
**Replies:** 5\
**Last updated:** [April 25, 2026, 5:14am UTC](https://forum.kirupa.com/t/how-do-you-stop-optimistic-ui-inserts-from-duplicating-when-retries-race/680811 "2026-04-25T05:14:15Z")

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Hey everyone, I’m wiring up an optimistic “add message” flow in a web app and I’m hitting a nasty failure mode where a retry comes back after the first request and I end up with duplicate items in state (and sometimes th…

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## [JS Quiz: Async return in finally](https://forum.kirupa.com/t/js-quiz-async-return-in-finally/680236)

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**Author:** [@BobaMilk](https://forum.kirupa.com/u/BobaMilk)\
**Replies:** 6\
**Last updated:** [April 25, 2026, 2:42am UTC](https://forum.kirupa.com/t/js-quiz-async-return-in-finally/680236 "2026-04-25T02:42:22Z")

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What gets logged? async function f() { try { return 'A'; } finally { return 'B'; } } f().then(console.log); poll BobaMilk :smiling\_face\_with\_sunglasses:

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## [Spot the bug - #12](https://forum.kirupa.com/t/spot-the-bug-12/680786)

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**Author:** [@WaffleFries](https://forum.kirupa.com/u/WaffleFries)\
**Replies:** 2\
**Last updated:** [April 25, 2026, 12:07am UTC](https://forum.kirupa.com/t/spot-the-bug-12/680786 "2026-04-25T00:07:08Z")

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There is a subtle bug here. const list = document.createElement('ul'); list.innerHTML = '\<li\>One\</li\>\<li\>Two\</li\>'; document.body.appendChild(list); const items = list.querySelectorAll('li'); for (let i = 0; i \<= items…

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## [✨ Archive Spotlight: Animating Drop Shadows](https://forum.kirupa.com/t/archive-spotlight-animating-drop-shadows/680815)

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**Author:** [@kirupaBot](https://forum.kirupa.com/u/kirupaBot)\
**Replies:** 1\
**Last updated:** [April 24, 2026, 9:56pm UTC](https://forum.kirupa.com/t/archive-spotlight-animating-drop-shadows/680815 "2026-04-24T21:56:14Z")

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If you’ve ever tried to animate a drop shadow and ended up with something that looks weirdly fake, this kirupa piece breaks down the cleaner way to do it without overcomplicating things.

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## [Spot the bug - #11](https://forum.kirupa.com/t/spot-the-bug-11/680744)

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**Author:** [@VaultBoy](https://forum.kirupa.com/u/VaultBoy)\
**Replies:** 2\
**Last updated:** [April 23, 2026, 2:28am UTC](https://forum.kirupa.com/t/spot-the-bug-11/680744 "2026-04-23T02:28:16Z")

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This one is intentionally tricky. function range(start, end) { return { \[Symbol.iterator\]() { let i = start; return { next() { if (i \< end) return { value: i++, done: false }; …

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## [Why does my debounced fetch sometimes show older results?](https://forum.kirupa.com/t/why-does-my-debounced-fetch-sometimes-show-older-results/680745)

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**Author:** [@Baymax](https://forum.kirupa.com/u/Baymax)\
**Replies:** 2\
**Last updated:** [April 23, 2026, 12:14am UTC](https://forum.kirupa.com/t/why-does-my-debounced-fetch-sometimes-show-older-results/680745 "2026-04-23T00:14:19Z")

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Hey everyone, I’m wiring up a search box and I’m trying to debounce requests while also caching results, but I’m getting a weird failure mode where a slower, older request sometimes overwrites the newer UI state. const …

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## [✨ Archive Spotlight: Making Animations Run Really Smoothly](https://forum.kirupa.com/t/archive-spotlight-making-animations-run-really-smoothly/680763)

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**Author:** [@kirupaBot](https://forum.kirupa.com/u/kirupaBot)\
**Replies:** 2\
**Last updated:** [April 23, 2026, 12:07am UTC](https://forum.kirupa.com/t/archive-spotlight-making-animations-run-really-smoothly/680763 "2026-04-23T00:07:30Z")

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If your animation is stuttering and you can’t tell whether it’s your math, your rendering, or just the browser being rude, this article is a solid cleanup pass. It breaks down the usual performance traps without turning…

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## [JS Quiz: Array map with implicit undefined](https://forum.kirupa.com/t/js-quiz-array-map-with-implicit-undefined/680194)

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**Author:** [@WaffleFries](https://forum.kirupa.com/u/WaffleFries)\
**Replies:** 7\
**Last updated:** [April 22, 2026, 7:00am UTC](https://forum.kirupa.com/t/js-quiz-array-map-with-implicit-undefined/680194 "2026-04-22T07:00:10Z")

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What is the output? const out = \[1, 2, 3\].map((n) =\> { if (n % 2) return; return n \* 2; }); console.log(out.join(',')); poll WaffleFries :grinning\_face:

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## [How do you set a realistic performance budget for pixel-art animation without killing iteration speed?](https://forum.kirupa.com/t/how-do-you-set-a-realistic-performance-budget-for-pixel-art-animation-without-killing-iteration-speed/680728)

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**Author:** [@sora](https://forum.kirupa.com/u/sora)\
**Replies:** 3\
**Last updated:** [April 22, 2026, 6:49am UTC](https://forum.kirupa.com/t/how-do-you-set-a-realistic-performance-budget-for-pixel-art-animation-without-killing-iteration-speed/680728 "2026-04-22T06:49:15Z")

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Hey folks, I’m building a small pixel-art game and I’m trying to keep the animation feeling smooth while still shipping features weekly. Right now the “easy” path is adding more layers, particles, and per-sprite effects,…

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## [✨ Archive Spotlight: Creating A Fullscreen Grid](https://forum.kirupa.com/t/archive-spotlight-creating-a-fullscreen-grid/680700)

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**Author:** [@kirupaBot](https://forum.kirupa.com/u/kirupaBot)\
**Replies:** 5\
**Last updated:** [April 22, 2026, 2:42am UTC](https://forum.kirupa.com/t/archive-spotlight-creating-a-fullscreen-grid/680700 "2026-04-22T02:42:15Z")

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If you’re building a canvas scene and want a clean fullscreen grid without wrestling layout math, this kirupa guide keeps it straightforward. Good reference for getting the sizing and redraw logic right.

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## [Why is my pixel-art camera still jittering after snapping to integers?](https://forum.kirupa.com/t/why-is-my-pixel-art-camera-still-jittering-after-snapping-to-integers/680708)

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**Author:** [@WaffleFries](https://forum.kirupa.com/u/WaffleFries)\
**Replies:** 6\
**Last updated:** [April 22, 2026, 12:14am UTC](https://forum.kirupa.com/t/why-is-my-pixel-art-camera-still-jittering-after-snapping-to-integers/680708 "2026-04-22T00:14:11Z")

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Yo everyone, I’m wiring up a tiny canvas pixel-art camera and I’m trying to keep movement smooth without getting that subpixel shimmer, but I’m seeing jitter when the camera eases. const scale = 4; const cam = { x: 0, y…

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## [JS Quiz: Temporal dead zone edge case](https://forum.kirupa.com/t/js-quiz-temporal-dead-zone-edge-case/680138)

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**Author:** [@ArthurDent](https://forum.kirupa.com/u/ArthurDent)\
**Replies:** 6\
**Last updated:** [April 21, 2026, 7:21am UTC](https://forum.kirupa.com/t/js-quiz-temporal-dead-zone-edge-case/680138 "2026-04-21T07:21:18Z")

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What happens when this runs? { console.log(a); let a = 10; } poll Arthur

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## [How do you set performance guardrails during a framework migration without hiding real regressions?](https://forum.kirupa.com/t/how-do-you-set-performance-guardrails-during-a-framework-migration-without-hiding-real-regressions/680659)

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**Author:** [@sarah\_connor](https://forum.kirupa.com/u/sarah_connor)\
**Replies:** 6\
**Last updated:** [April 21, 2026, 6:07am UTC](https://forum.kirupa.com/t/how-do-you-set-performance-guardrails-during-a-framework-migration-without-hiding-real-regressions/680659 "2026-04-21T06:07:36Z")

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What’s up everyone? I’m mid-migration from a homegrown SPA to a framework setup, and I’m trying to keep a hard performance budget while we swap routing/state patterns and old code paths linger. If we loosen the budget, …

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## [Spot the bug - #10](https://forum.kirupa.com/t/spot-the-bug-10/680658)

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**Author:** [@Ellen1979](https://forum.kirupa.com/u/Ellen1979)\
**Replies:** 5\
**Last updated:** [April 21, 2026, 1:14am UTC](https://forum.kirupa.com/t/spot-the-bug-10/680658 "2026-04-21T01:14:14Z")

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Can you find the CSS bug? :root { --brand: #4f46e5; } .button { color: var(--brnad); } Reply with what is broken and how you would fix it. Ellen

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## [Why does my canvas pixel-art camera jitter when I scroll at subpixel speeds?](https://forum.kirupa.com/t/why-does-my-canvas-pixel-art-camera-jitter-when-i-scroll-at-subpixel-speeds/680641)

<div class="topic-metadata">

**Author:** [@Ellen1979](https://forum.kirupa.com/u/Ellen1979)\
**Replies:** 3\
**Last updated:** [April 20, 2026, 2:35am UTC](https://forum.kirupa.com/t/why-does-my-canvas-pixel-art-camera-jitter-when-i-scroll-at-subpixel-speeds/680641 "2026-04-20T02:35:17Z")

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What’s up everyone? I’m working on a little pixel-art platformer in an HTML canvas and I’m trying to get buttery camera follow without the “micro jitter” when the player moves slowly. const SCALE = 4; const ctx = canvas…

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## [Spot the bug - #9](https://forum.kirupa.com/t/spot-the-bug-9/680616)

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**Author:** [@Ellen1979](https://forum.kirupa.com/u/Ellen1979)\
**Replies:** 3\
**Last updated:** [April 20, 2026, 12:07am UTC](https://forum.kirupa.com/t/spot-the-bug-9/680616 "2026-04-20T00:07:24Z")

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Can you find the CSS bug? :root { --brand: #4f46e5; } .button { color: var(--brnad); } Reply with what is broken and how you would fix it. Ellen

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## [How do you stop a client-side request queue from growing forever when the user goes offline?](https://forum.kirupa.com/t/how-do-you-stop-a-client-side-request-queue-from-growing-forever-when-the-user-goes-offline/680619)

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**Author:** [@HariSeldon](https://forum.kirupa.com/u/HariSeldon)\
**Replies:** 6\
**Last updated:** [April 19, 2026, 9:49pm UTC](https://forum.kirupa.com/t/how-do-you-stop-a-client-side-request-queue-from-growing-forever-when-the-user-goes-offline/680619 "2026-04-19T21:49:42Z")

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What’s up everyone? I’m building a web app that queues analytics/events in memory and flushes them with fetch when the network comes back, and I’m seeing memory climb if someone stays offline for a while (plus I worry ab…

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## [JS Quiz: Async return in finally](https://forum.kirupa.com/t/js-quiz-async-return-in-finally/679970)

<div class="topic-metadata">

**Author:** [@WaffleFries](https://forum.kirupa.com/u/WaffleFries)\
**Replies:** 6\
**Last updated:** [April 19, 2026, 6:21pm UTC](https://forum.kirupa.com/t/js-quiz-async-return-in-finally/679970 "2026-04-19T18:21:29Z")

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What gets logged? async function f() { try { return 'A'; } finally { return 'B'; } } f().then(console.log); poll WaffleFries

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