[Feature Request] Add loading class for navigating between gallery images

[dbworth]

If using the Gallery for images with a large file size, it would be useful to have the option of displaying a loading animation when you click the "next" or "previous" buttons.

A previous solution was to always display the animation in the background:
https://stackoverflow.com/questions/49582414/featherlight-gallery-doesnt-display-loader-animation-loading-next-image-lightb/49583318#49583318

Here is my attempt to toggle the loading class when navigating in the gallery:
PR #355

To see the result, look here:
Down in the bottom-right you can see 3 images.
Click the middle image and a loading animation will display (current behaviour).
Click "previous" and the loading animation will display again (new behaviour).
http://jsfiddle.net/cvjxydfd/

I called the class "loading-gallery" so it doesn't change existing functionality for current users, and allows new users the choice.

I welcome any alternative ideas or suggestions to improve this PR.

[marcandre]

Thanks for the report & PR.
I was wondering: wouldn't the existing "loading" class be sufficient? (i.e. instead of setting it it once as it is currently, it should be set whenever the content change)

[dbworth]

Yes you could also use the existing "loading" class. That's ok with me.
I was worried that maybe some users preferred the existing behaviour, and such a change would alter that existing behaviour if they upgraded the library.

[marcandre]

Right. Still, I think it's semantically correct to have the 'loading' class toggle while the content is loading, no matter if it's the first load or subsequent ones. Would you like to tweak your PR?

[dbworth]

No worries, I updated the PR #355
and the test:
http://jsfiddle.net/zehu9vge/