Heavy JavaScript codebase

Problem Summary

A heavy JavaScript codebase forces browsers to download, parse, compile, and execute more code than the page needs.

Performance Impact

• Slow interactivity: Main-thread execution blocks user input
• Poor INP: Event handlers wait behind long JavaScript tasks
• Higher mobile cost: Low-end devices parse and execute code slowly
• Delayed rendering: Render-blocking scripts postpone visible content

How to Detect

1. Coverage tab: Identify unused JavaScript
2. Lighthouse: Review JavaScript execution time and unused code
3. Network waterfall: Check bundle size and blocking scripts

Solutions

1. Remove Unused Libraries

Audit plugins, theme features, and tracking scripts that add frontend JavaScript.

2. Load Scripts Per Page

Only enqueue scripts on pages where they are actually used.

3. Defer Noncritical Scripts

<script src="/assets/app.js" defer></script>

4. Split Large Bundles

Load interactive features only when the related component appears.