Depends on how you use it and on how much elements. I am not sure if this is even worth to be a library. Sometimes I am wondering why people want to use a lib for everything.

I agree, many times a library isn't necessary. In backbone.js I solved this with an interval triggering a global event which sends current scroll pos to all listening views.

If it's not my own code, it's worth being a library.

And I don't want to spend my time learning to write it correctly to handle all case and be performant.

Any time you're performing an operation on a scroll event, that is a risk. But this uses a single "scroll" event listener throttled to fire a maximum of every 100ms.

https://github.com/camwiegert/in-view/blob/master/src/in-vie...