How to Find and Fix 7 Hidden Performance Bottlenecks in Your JavaScript Code

Short summary

This article identifies 7 common JavaScript performance bottlenecks—layout thrashing, unbounded listeners, DOM reads in loops, missing requestAnimationFrame, JSON parsing, CSS selector complexity, and unoptimized bundles—with detection strategies using Chrome DevTools. Each bottleneck includes specific fixes like batching DOM operations, cleaning listeners with AbortController, and caching layout values. Implementing these improves Core Web Vitals scores and reduces rendering and painting time.

• •7 JavaScript bottlenecks cause 73% of performance issues: layout thrashing (40-60% slowdown), unbounded listeners, synchronous DOM reads, missing animation batching, JSON parsing, CSS selector complexity, and unoptimized bundles
• •Detection uses Chrome DevTools Performance panel; fixes involve batching reads/writes, AbortController for listener cleanup, caching layout values, and requestAnimationFrame for scroll handlers
• •Measured improvements in Core Web Vitals (LCP, INP) by addressing how code interacts with the browser rendering pipeline

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