methodology / Performance / #38
Largest unused JavaScript bundle
#38 · Recommended · Web Quality · weighted · Performance · weight 0.7% · impl implemented · method v1.2.0
Web Quality factor
This factor is part of Web Quality — the weighted 0..100 score that sits above Web Standards. Its weight depends on what kind of site is being measured. Web Standards items take priority; this factor only enters the score once Web Standards passes.
- Base weight
- 0.7 applied to every site type unless overridden below
- Why this weight
- Unused JavaScript bloat — main contributor to slow first-loads.
Per-site-type overrides
| Site type | Weight | Δ vs base |
|---|---|---|
| News / Publisher | 0.9 | +0.2 |
| Personal site | 0.4 | -0.3 |
| Media / Streaming | 0.9 | +0.2 |
Site types not listed inherit the base weight.
What this means for your business
Themes and page builders often ship piles of features your site never uses, and the visitor's phone has to download all of it anyway. Trimming this is the single biggest speed win on most small-business sites.
Plain title: You're not shipping code visitors don't use
What we measure
Pages often ship code that visitors never actually use. Unused JavaScript still has to be downloaded, parsed, and compiled, slowing rendering on mobile devices.
How to improve your score
Code-split by route so each page only loads its own JS, defer non-critical scripts, and audit third-party scripts for ones you can remove.
Facts
Implementation notes
Pull the `unused-javascript` audit from the PSI Lighthouse audits array and surface the largest offender.
Scoring
Scoring formulas are versioned with the methodology. The current method (v1.2.0) maps raw measurements to pass, warn, fail. Factor weights determine how much each contributes to the composite — see the methodology index for the full table.
Version history
| Version | Change | Date |
|---|---|---|
| v1.2.0 | Factor introduced. Status: live. Scoring impl: implemented. | 2026-04-25 |