Passive listeners are a relatively new concept in web development that was released in 2016. Passive listeners allow for better scrolling performance. You may not realize the importance today, but before passive listeners were introduced, users had to wait until the page was loaded before they could begin scrolling via touch or mouse. Additionally, users could only scroll so far until the page had to stop.
Use Passive Listeners to Improve Scrolling Performance
What are Passive Listeners?
How to Use Passive Listeners
Today, with a flick of your finger, you can scroll all the way through a page before it stops. This offers users a smoother and better overall experience, by removing the stops and stutters that would otherwise occur in previous browser versions. Lighthouse flag this audit if it detects any lines where are not set with passive listeners. By introducing the passive: true attribute, developers can tell the browser to begin scrolling immediately, as opposed to having to wait until the script finishes executing.
Lighthouse is an open-source tool that is used to run an audit against your web pages and provides scores and suggestions for improving page performance, accessibility, SEO, and more.
PageSpeed Insights is a tool created by Google that reports on the performance of a page on both mobile and desktop devices, and provides suggestions on how that page may be improved.