Drag-and-dropping a file directly on the HTML `<input type="file">` file picker works with no code/JS.

If you want to splash up the "drop here" thing it's a frickin nightmare. The events don't fire when they should (e.g. mouse leave doesn't fire so it gets stuck, or you get duplicate events or missing events) so you get a bunch of flicker unless you do a bunch of debouncing and fail safes to cover all the browser quirkiness. And this is the easy drop-a-file scenario.

Doing all the stuff shown in https://www.youtube.com/watch?v=l7v-UwpsEbk I'm not sure I'd even know where to begin.