Performance fix guide
Significant Unused JavaScript
A large portion of downloaded JavaScript is never executed during page load. This wastes bandwidth and increases parse/compile time.
Issue ID: CWV-UNUSED-JS-001
Severity: moderate
Impact: Med
Effort: M
Use this article when
- You need deeper remediation guidance than the issue card can show.
- You want CMS-specific steps before handing the fix to a developer.
- You want a repeatable re-check path after shipping the change.
What this issue is
A large portion of downloaded JavaScript is never executed during page load. This wastes bandwidth and increases parse/compile time.
Why it matters
A large portion of downloaded JavaScript is never executed during page load. This wastes bandwidth and increases parse/compile time. This affects load speed, Core Web Vitals, and how many visitors stay long enough to convert.
How we detect it
- FreeSiteAudit flags this issue when the rule for CWV-UNUSED-JS-001 fails and the page evidence points to Performance tool.
- You can usually confirm this by checking the page source or the relevant page settings inside your CMS.
Evidence examples
Check the affected page source, rendered output, or relevant CMS setting to confirm the missing or incorrect element.
How to fix it
- 1Use Chrome DevTools Coverage tab to identify unused code
- 2Implement code splitting to load only what is needed
- 3Remove unused libraries and polyfills
- 4Use tree-shaking in your bundler
How to re-check it
- Check Coverage tab in DevTools and confirm unused JS is reduced
Related tools
This issue is best verified with the full FreeSiteAudit crawl rather than a single-point mini tool.