I can't think of a single website I know that uses JS to intelligently load thing via connection-speed sniffing. It's a nice thought, but it doesn't happen. The

I can't think of a single website I know that uses JS to intelligently load thing via connection-speed sniffing. It's a nice thought, but it doesn't happen. There used to be JS fills for responsive imagery -- it was never connection-speed based, but viewport based -- but this is all browser-native these days. Some things might provide simpler assets via CDN-based UA sniffing.