Meant for displaying before and after screenshots of websites, this side-by-side scrubber works really well, and includes a nav for swapping in additional photos. Since originally pitching this interaction, I've seen implementations much more commonly, but I wrote this before there were quite so many around to crib from.
There are two key JS files at work here. The first one sets up the scrubbing interaction and image swapping with a nice little class-like factory. I'm still pleased with how this works whenever I interact with it. The other one does srcset things with background images. This was definitely a rabbit hole when it happened, but I kind of liked the flexibility of it, and tried to make sure it was generically callable so I could roll it out all over the site. It does have the negative effect of downloading a useless small image on larger screens, but it's smart enough to know when it's already got a large enough image and won't swap sizes down (if you're a developer and are shrinking your browser window, say).
There is a little bit of weirdness in the template because I was trying to unload ACF on the front-end to juice performance a little extra and wrote my own helper functions to get the data directly out of post_meta. But if you squint a little and look past that, the logic for displaying everything is simple and concise.
I really appreciate the visual phone gag in the images here, though I felt very old when the designers didn't understand my "Zack Morris phone" reference and had to Google for what cellphone bricks used to look like....