Infinite Scroller is challenging, Chrome has added it to Built In Modules.
To be short, Infinite Scroller tries to render only the element within the viewport while it being scrolled, which means to remove the invisible element from the DOM
Here is a nice video about it :
And here is an article from Google Complexities of an Infinite Scroller
Show us how would you implement by yourself, what the performance challenge is and how would you tackle it.