Google is testing changes to the JavaScript timers for background tabs in Chrome that improve battery usage by 13% to 28%. Users can enable the feature in the Canary version of Chrome and Edge.

Chrome JavaScript timer throttling: Google's tests show it saves up to 2 hours' battery life Chrome will soon throttle JavaScript timers in the background, so the browser uses significantly less ...

Executing JavaScript code will definitely involve the processor cache and a high-resolution timer is accessible via browser performance API.