JavaScript the page downloads but never uses Lighthouse: Reduce unused JavaScript · Est savings of 5,097 KiB · could save about 14.4 s
The phone's processor is kept busy for seconds Lighthouse: Minimize main-thread work · 26.7 s · could save about 9.9 s
Scripts take a long time to run on a phone Lighthouse: Reduce JavaScript execution time · 20.4 s · could save about 7.4 s
What it costs
Google calls 2.5 s or less good for the main content. ulta.com is more than 18 s past that on a mid-range phone.
Speed is money: in Deloitte's 2020 study Milliseconds Make Millions (37 brands, 30 million sessions), making a site just 0.1 s faster on phones went with 8.4% more orders for retail sites and 10.1% for travel sites. Most slow pages come down to one or two root causes.
Want it fixed?
We find the root cause across the browser, the network and the server, fix it,
and prove it with a before-and-after test. Start with a Diagnosis: a written root cause and a fix plan.