RUM update: lux.js v308

24 May 2023 (UTC)

New features

  • Pages that are prerendered are now flagged as such.
  • Pages that are restored from the back-forward cache (bfcache) can now be tracked by setting LUX.newBeaconOnPageShow = true. Read the documentation for more information on how this works.
  • Server timing metrics are now extracted from the main page response. Metrics must be configured in your SpeedCurve settings before they are collected.


  • The beacon will no longer be sent automatically if the page visibility is hidden. This can be overridden by setting LUX.trackHiddenPages = true.
  • All metrics on prerendered pages are now relative to activationStart.
  • Navigation timing values with a value of zero are now reported, rather than ignored.
  • The legacy domLoading metric is no longer collected.
  • The first paint event of any type will be considered for start render, rather than just first-paint events.

Bug fixes

  • Timing values are now rounded down to the nearest unit to prevent values from being rounded into the future.