Dbox is an image lightbox written in es6 that leverages HTML5 dialog element and mimics Twitters image lightbox by applying an images dominant color to it's background.
Lazy loading images with the "new" Intersection Observer API. It's super easy and very few lines of Javascript and introducing IOLazy intersection observer lazy load library.
Using the Save-Data client hint with Bolt BetterThumbs to send smaller images to users on low bandwidth or slow connections
With Chrome now supporting Animated PNG as of Chrome 59 we have two image formats that can supplant the old and tired GIF format. Varying posts and sites have different conclusions on when to use APNG versus an animated Webp. In all my findings (linked below where the source Gif comes from) animated webp beats apng in filesize each and every time. Sometimes by not very much.
Opmitimizing MP4 and WebM videos for the web and converting MP4 to WebM