---
phase: 08-frontend-performance-ux
plan: 03
subsystem: frontend
tags: [lit, classMap, performance, render-optimization, directives]

# Dependency graph
requires:
  - phase: 08-frontend-performance-ux
    provides: "repeat() directive migration on all virtualizer instances"
provides:
  - "classMap directive for conditional CSS classes in track-list renderTrackRow and queue-panel renderTrackItem"
  - "Search highlight short-circuit when search term is empty"
  - "Hoisted search term lookup outside per-column iteration loop"
affects: [08-frontend-performance-ux]

# Tech tracking
tech-stack:
  added: []
  patterns: ["classMap directive for conditional CSS classes in render hot paths"]

key-files:
  created: []
  modified:
    - frontend/src/components/track-list/track-list.ts
    - frontend/src/components/queue-panel/queue-panel.ts

key-decisions:
  - "classMap object literal per-call is acceptable — classMap internally diffs and only updates changed classes"
  - "Hoisted searchCtrl.term outside cols.map to avoid repeated property access per column"

patterns-established:
  - "Render hot path pattern: use classMap directive instead of array filter/join for conditional CSS classes"

requirements-completed: [PERF-05, UX-02]

# Metrics
duration: 2min
completed: 2026-03-05
---

# Phase 8 Plan 03: renderTrackRow Optimization Summary

**Replaced array filter/join class construction with classMap directive in track-list and queue-panel render hot paths, eliminating per-row array allocations during scrolling**

## Performance

- **Duration:** 2 min
- **Started:** 2026-03-05T04:19:55Z
- **Completed:** 2026-03-05T04:22:19Z
- **Tasks:** 2
- **Files modified:** 2

## Accomplishments
- All conditional CSS class construction in renderTrackRow (track-row, fav-icon, cell) converted from array filter/join to classMap directive
- Queue-panel renderTrackItem class construction (track-item, active, selected, drop-before, drop-after) converted to classMap
- Search term property lookup hoisted outside per-column loop to avoid repeated access
- Search highlighting already short-circuits when term is empty — no additional optimization needed

## Task Commits

Each task was committed atomically:

1. **Task 1: Replace class string construction with classMap directive in renderTrackRow** - `ad21027` (perf)
2. **Task 2: Optimize column value computation and apply classMap to queue-panel renderTrackItem** - `62f41c2` (perf)

## Files Created/Modified
- `frontend/src/components/track-list/track-list.ts` - classMap for track-row, fav-icon, and cell classes; hoisted search term lookup
- `frontend/src/components/queue-panel/queue-panel.ts` - classMap for track-item with active, selected, drop-before, drop-after states

## Decisions Made
- classMap object literal allocation per-call is acceptable since classMap internally diffs previous values and only applies DOM changes for actually changed classes — net benefit over string concatenation in Lit's update cycle
- Hoisted searchCtrl.term outside the cols.map loop — avoids redundant property access per column per row

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered
None

## User Setup Required
None - no external service configuration required.

## Next Phase Readiness
- All render hot path optimizations complete for track-list and queue-panel
- Ready for Plan 04 (final phase 8 plan)

## Self-Check: PASSED

All key files exist on disk. All task commits verified in git history.

---
*Phase: 08-frontend-performance-ux*
*Completed: 2026-03-05*