Add class when user scrolls below the sticky container

[SaFrMo]

Adds a class when the user scrolls past the container, leaving the sticky element at the bottom of the sticky-container.

[patrickbolle]

Hi there, when would this be useful?
I'm having an issue with sticky-js where the sticky part goes floats overtop a lower section, would adding a class here help me to stop that from happening?

Thanks @SaFrMo !!

[SaFrMo]

@patrickbolle Hey! I had some elements I wanted to fade out when the sticky element reached the bottom of its container. This pull request makes that easy with just CSS:

.sticky-element .to-fade-out { 
    opacity: 1;
}

.sticky-element.stuck-bottom .to-fade-out {
    opacity: 0;
}

I don't think this is going to help in your case - it'd be best, if possible, to size the sticky-container so that it doesn't run over the lower section, or to use overflow:hidden on the sticky-container. You might be able to do some fading or z-indexing to fix your situation, too.

[SaFrMo]

Added additional ability to create a sibling placeholder instead of wrapping the sticky element: new Sticky({ sibling: true }).

Wrapping sticky elements with iframes as children forces the iframes to be re-rendered, but doing so broke the iframe's content with Google DFP ads. I copied the functionality of the wrapping function and made it work the same way on a sibling span, which works as a placeholder without rerendering content.

[jamsinclair]

@SaFrMo Just want to throw some thanks your way. Your fork with these features makes this library 😍 👌

[SaFrMo]

Thanks @jamsinclair ! 😄