'Reduce unused JavaScript' is a warning you'll encounter in Lighthouse-based web performance auditing tools, such as the local Lighthouse tool in Chrome DevTools, PageSpeed Insights, and DebugBear.
Unused JavaScript harms web performance because it slows down your page without providing any tangible benefits. It's like taking a bunch of clothes you won't need for a trip but still having to carry them around and paying a higher baggage fee on the plane.
To optimize your site for web performance and improve Core Web Vitals, you need to find a way to reduce unused JavaScript on your site. In this tutorial, we'll look into some hands-on techniques you can use to achieve this goal.