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MakeFaster: cut Lighthouse LCP ~73% cold / ~70% warm (6 kept experiments) by jjcm · Pull Request #1 · makefaster-dev/algorithm-visualizer · GitHub

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MakeFaster: cut Lighthouse LCP ~73% cold / ~70% warm (6 kept experiments) - #1

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MakeFaster: cut Lighthouse LCP ~73% cold / ~70% warm (6 kept experiments)#1
jjcm wants to merge 6 commits into
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jjcm commented Aug 26, 2026

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Summary

Experimental render-performance loop (MakeFaster) run against the production build of this fork, served locally. North star: Lighthouse LCP (v13.4.1, simulated mobile throttling, median of 3 runs per condition, cold + warm).

metric baseline final delta
cold LCP 13,822 ms 3,687 ms −73.3%
warm LCP 12,318 ms 3,683 ms −70.1%
cold TTI 14,844 ms 7,149 ms −51.8%
perf score (cold) 53 87 +34

Kept changes (one commit each)

  1. Precompress static assets — scripts/compress-build.js runs after react-scripts build and emits gzip + brotli siblings for the text assets in build/ (vendor chunk 2,027 KB → 407 KB brotli). Any static host that serves compressed siblings picks them up (e.g. nginx gzip_static/brotli_static, http-server -g --brotli). Measured: −60.8% cold LCP.
  2. Cut critical-path JavaScript — chart.js + moment (~206 KB raw) load via dynamic import only when a chart/scatter visualization actually renders; the home route never fetches them. −5.5% cold LCP.
  3. Inline critical HTML shell — public/index.html paints the app frame and the home intro paragraph (the LCP element) from static HTML+CSS before the bundle mounts; React replaces it on mount, and an inline script hides it on deep links. −8.7% cold LCP, warm FCP 3,176 → 755 ms.
  4. Defer analytics loading — the tag script is injected on the load event instead of an async <head> script, so it no longer competes with render-critical resources (the stub queue still records early events). −12.6% cold LCP.
  5. Self-host the interface font — replaces the render-blocking fonts.googleapis.com stylesheet + fonts.gstatic.com fetch with an inline @font-face over a same-origin woff2 (one variable-width latin file covers weights 400/700). −11.4% cold LCP, cold FCP 3,116 → 759 ms.
  6. Lazy-load the code editor — with the LCP now painted from the static shell, the ace editor (64% of the vendor bundle) moves to a lazy chunk; entry vendor 457 KB → 129 KB gzip. −40.3% warm LCP, cold flat within noise.

Tried and reverted (by the numbers)

  • Lazy editor before the HTML shell keep (+16% cold LCP — the boot-time chunk was chained into the LCP graph)
  • Inline the shared stylesheet (+9.6% — heavier document outweighed the saved round trip)
  • loading="lazy" on markdown images (−0.7%, below the noise floor)
  • font-display: swap alone (−0.7% — the web-font repaint forms a larger, later LCP candidate)
  • Metric-matched fallback font (no change)
  • Preload the critical font (+9.7% — stole bandwidth from render-blocking resources)
  • Drop bluebird for native promises (no measurable LCP change)

Notes

  • Experimental branch for the MakeFaster loop on this fork only; not intended for upstream as-is.
  • The self-hosted font ships the latin subset (the UI and entry content); other scripts fall back to the system sans-serif stack.
  • The static shell mirrors the home route and is hidden by an inline script when booting a deep link, so algorithm/scratch-paper URLs never flash home content.
  

jjcm marked this pull request as ready for review August 26, 2026 00:16
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