What happens when you scroll up/down a page?
Does the page stay as it is as it moves out of your screen's borders or does it delete itself for resource purposes?
I just thought that while scrolling through devRant and YouTube (which I do all the time).

It's very complicated. Every browser handles rendering its own way - and every site is capable of running scripts to optimize scrolling.

Most modern browsers manage a CSSOM and decide how to render based on that. Some of screen rendering is "ignored" until visible.

@GhostInTheShell Thanks, I never really thought about what happens past the screen so I thought I'd ask now.

I once made a 10 km long white web page because I was curious to see how browsers would handle it. It was quite interesting. To my surprise, ie actually had the best results not being affected at all by the long page while Firefox got slow and chrome started to render strange artifacts as I scrolled down.
This was a few years ago so maybe the results would be different today.

There's actually a great (free) course on Udacity on Website Performance Optimization about how browsers render pages. Would definitely recommend it to any web developer.
https://udacity.com/course/...

@Olverine how do you convert page length to kilometers? Is that like a metric thing :P

@stevenliemberg You use cm (centimeters) as units in css. 1km = 100 000cm