Epic 4.3: Frontend Performance Optimization

[test3207]

Overview

Frontend performance optimization based on Lighthouse audit results.

Test URL: https://m3w.test3207.fun/
Initial Test Date: 2025-12-20
Lighthouse Version: 13.0.1

✅ Results Achieved

Category	Before	After	Status
Performance	43%	100%	✅ Perfect
Accessibility	88%	100%	✅ Perfect
Best Practices	100%	100%	✅ Perfect
SEO	91%	100%	✅ Perfect

Key Performance Metrics

Metric	Before	After	Target	Status
LCP (Largest Contentful Paint)	9.4s	~0.3s	< 2.5s	✅ Exceeded
FCP (First Contentful Paint)	3.3s	~0.3s	< 1.8s	✅ Exceeded
TBT (Total Blocking Time)	930ms	0ms	< 200ms	✅ Exceeded
Speed Index	6.0s	~0.5s	< 3.4s	✅ Exceeded
TTI (Time to Interactive)	9.4s	~0.5s	< 3.8s	✅ Exceeded
CLS (Cumulative Layout Shift)	0	0	< 0.1	✅ Good

Sub-Issues

Critical (P0)

• Improve LCP from 9.4s to < 2.5s #227 Improve LCP from 9.4s to < 2.5s (closed: resolved in PR perf(frontend): improve LCP with critical CSS inlining and async loading #255, perf: optimize frontend performance, a11y, and SEO (Lighthouse 100) #257)

High Priority (P1)

• Reduce TBT from 930ms to < 200ms #221 Reduce TBT from 930ms to < 200ms (closed: resolved in PR perf: lazy-load cache-manager to reduce initial bundle size #256, perf: optimize frontend performance, a11y, and SEO (Lighthouse 100) #257)
• Improve FCP from 3.3s to < 1.8s #220 Improve FCP from 3.3s to < 1.8s (closed: resolved in PR perf(frontend): improve LCP with critical CSS inlining and async loading #255, perf: optimize frontend performance, a11y, and SEO (Lighthouse 100) #257)

Medium Priority (P2)

• Optimize static assets (favicon 1MB, images) #222 Optimize static assets (favicon 1MB, images) (closed: resolved in earlier PRs)
• Remove unused JavaScript (~888KB savings) #228 Remove unused JavaScript (~888KB savings) (closed: resolved in PR perf(frontend): improve LCP with critical CSS inlining and async loading #255, perf: lazy-load cache-manager to reduce initial bundle size #256)
• perf: reduce main bundle via shared subpath exports #261 Reduce main bundle via shared subpath exports

Implementation Summary

PR #255: Code Splitting & Lazy Loading

• Route-based code splitting with React.lazy()
• Component lazy loading for modals/drawers
• Bundle analysis and optimization

PR #256: Lazy-Load Cache Manager

• Defer cache-manager initialization to idle time
• Reduce initial bundle size

PR #257: Optimize HTTP Requests & Core Web Vitals

• Merge small chunks (51 → 16 JS files, -69%)
• Unified idle task scheduler with adaptive delays
• Pre-render homepage content for instant LCP
• Async CSS loading plugin
• SEO improvements (robots.txt)
• Accessibility improvements (main landmark, heading hierarchy, aria labels)
• Service Worker optimizations (cache GitHub avatars)

PR #260: Shared Package Subpath Exports (pending)

• Add subpath exports to @m3w/shared
• Remove hash from barrel export
• Lazy load MobileLayout, PWA prompts
• Main bundle: 354KB → 293KB (-17%)

Technical Approach Applied

1. ✅ Code Splitting: Route-based + component-level lazy loading
2. ✅ Lazy Loading: Deferred modals, drawers, and background services
3. ✅ Bundle Analysis: Reduced from 51 to 16 JS files
4. ✅ Asset Optimization: Compressed favicon, optimized images
5. ✅ Pre-rendering: Homepage content in index.html for instant LCP
6. ✅ Async CSS: Non-blocking stylesheet loading
7. ✅ Idle Task Scheduling: Background tasks deferred until after load

Success Criteria

• Performance score > 80% → Achieved: 100%
• LCP < 2.5s → Achieved: ~0.3s
• TBT < 200ms → Achieved: 0ms
• FCP < 1.8s → Achieved: ~0.3s
• All Core Web Vitals pass → All green

Related PRs

• perf(frontend): improve LCP with critical CSS inlining and async loading #255 - Code splitting and lazy loading
• perf: lazy-load cache-manager to reduce initial bundle size #256 - Lazy-load cache-manager
• perf: optimize frontend performance, a11y, and SEO (Lighthouse 100) #257 - HTTP request optimization, a11y, SEO
• perf: reduce main bundle via shared subpath exports #260 - Shared package subpath exports (pending)

Milestone

Milestone 4: Feature and Infra Enhancements