restrict file types

You can use the OnSelect client-side event to prevent the selection of files with invalid extensions. The handler validation is still required.

Note that you have to cancel the selection of all files if more than one is chosen at one go.

Oops, wrong link, sorry! Try this one.

The select event will fire when you drop files as well. Same code applies without change.

I did a quick test in Chrome. the list of dragged files is not available in the dragover and dragenter DOM events. It is populated only when the actual drop occurs.

In short, we don't know what's being dragged until it's dropped.