optimize React app performance

[Mariannadtd]

React Performance

Task

React: Performance

Deploy

N/A — deploy is not required for this task. Performance report with profiling screenshots is included in the repository.

Screenshots

Baseline

Optimized

More screenshots and detailed measurements are available in PERFORMANCE.md.

Done

16.06.2026

Score

100 / 100

Self-check

• Initial profiling documented with screenshots — 15 / 15
• useMemo used for computed values — 12 / 12
• useCallback used for event handlers — 12 / 12
• React.memo used to prevent unnecessary re-renders — 12 / 12
• Proper key props used for lists and tables — 12 / 12
• Virtualization implemented for large country list — 22 / 22
• Final profiling documented with comparison to baseline — 15 / 15

Performance Results

Interaction	Before	After	Improvement
Sorting countries	451.7 ms	4.4 ms	99.0%
Searching for a country	216.6 ms	7.8 ms	96.4%
Selecting a different year	37.1 ms	20.2 ms	45.6%
Toggling columns	53.2 ms	8.9 ms	83.3%

Checks

• npm run lint
• npm run build