Removed getBoundingClientRect + Controlled Scroll support

[MaartenBruggink]

Hi @thebuilder, first of all thanks for this great library!

In this pull request there are two changes that intertwine a bit.

1. I noticed a node.getBoundingClientRect() on every scroll tick, this could be quite heavy performance wise so I changed these to a combination of node.offsetTop and node.offsetHeight and the corresponding for the horizontal axis.

2. This changes was needed to make this library work with a controlled scroll. This can be quite useful for sliders or websites that feature a form of smooth scrolling.

In this fork are still some Typescript related issues. I wanted to discues the nature of these changes first before diving into Typescript more.

Please let me know what you think!

[thebuilder]

Hey @MaartenBruggink

I'm not sure I fully understand what the *Controlled scroll does. Can you explain this?
I'm aware that using getBoundingClientRect has a slight cost, but I haven't noticed in performance issues in implementations.

A problem with using offsetTop is that it doesn't account for the parent's offset. I think this could be a potential issue - depending on the nested level of the element. You'd have to do a recursive loop through all the parent elements, and by then it's properly better to just use getBoundingClientRect.

Another solution could be to throttle the the update - So it only fires something like every 50ms. This should be a value that can be controlled by the options.

[thebuilder]

I'm using yarn for the project, so i would prefer if it wasn't changed to npm

[thebuilder]

Is there a reason for this change?

[MaartenBruggink]

Hey @thebuilder

Controlled in the way that we own the scroll value in the React State. This way you could make horizontal slider work with a transform value instead of an element with a scrollbar.

I see the issue with the offsetTop, in the tests in StoryBook I didn't have any issues with offsetTop. I'll try to make a case where the parent has a transform value.

The change from yarn to npm should be changed back and the strict false is because of my limited knowledge in Typescript. I wanted to be able to discus these changes with you before cleaning up the Typescript interfaces.