methodology / Performance / #38

Largest unused JavaScript bundle

live factor #38 · Performance · scoring impl: implemented · weight 0.7%

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.

Data source

Data source for this factor is not yet documented.

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 (v1.1.0) 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

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