Make scrolling other elements trigger lazy-loading

[zaccharles]

This PR fixes a problem I currently have. Simply, I have a div on my page which is overflow: auto. Inside this div, I have a bunch of images that I want to lazy-load with Layzr. The issue is that Layzr's handlers method only operates on window. This means that only scrolling the window itself will trigger lazy-loading, and scrolling any other element won't. I propose the addition of handlersFor which will add the scroll handler for the given node.

Note: I looked into detecting resizing of a div (though, it's not a problem I have). It seems that this is a popular solution, and very efficient. However, it would introduce a dependency for an edge case which is probably rare. Having said that, maybe we should expose requestFrame (perhaps under a different name) as a hook for adding other triggers?

[callmecavs]

@zaccharles I like the idea. I think for a cleaner implementation though, it might make more sense to extend the current handler method. If it accepted an additional parameter, that was a selector or element node (and defaulted to the window object if not passed in), it would keep the code DRYer, and accomplish the same thing.

I'll look into this in the near future, when I get some time to potentially cut a release. I also want to do some testing, to make sure the existing in viewport calculation will work for elements that are inside scrolling containers, rather than a scrolling window.

[zaccharles]

I think that sounds like a better solution.

As for the in viewport calculation, I can tell you that it worked on my app, so at least there's some promise :) I also exposed requestFrame in my fork and found it quite useful to have access the that.

Anyway, I'll continue using my fork for now, happy to help if I can, though I think you're all over it :)

[callmecavs]

cheers man 🍻 hopefully I'll get a chance to take a look this weekend - if not definitely next week. glad to hear that this is working in your fork, praying I wont have to rework anything haha

[iztsv]

Hello @callmecavs and @zaccharles
As I can see this branch has conflicts.

@zaccharles are you planning to resolve conflicts?

Or in another way I can create new pull request for the same feature with my code and tests. What do you think about it?

[zaccharles]

Happy for you to create a new PR @ilyaztsv :)

[iztsv]

@zaccharles I created PR regarding to optional container with scroll.