Prevent browser from loading a drag-and-dropped file

Question

I\'m adding an html5 drag and drop uploader to my page.

When a file is dropped into the upload area, everything works great.

However, if I accidentally drop

Answer 1

Preventing all drag and drop operations by default might not be what you want. It's possible to check if the drag source is an external file, at least in some browsers. I've included a function to check if the drag source is an external file in this StackOverflow answer.

Modifying Digital Plane's answer, you could do something like this:

function isDragSourceExternalFile() {
     // Defined here: 
     // https://stackoverflow.com/a/32044172/395461
}

window.addEventListener("dragover",function(e){
    e = e || event;
    var IsFile = isDragSourceExternalFile(e.originalEvent.dataTransfer);
    if (IsFile) e.preventDefault();
},false);
window.addEventListener("drop",function(e){
    e = e || event;
    var IsFile = isDragSourceExternalFile(e.originalEvent.dataTransfer);
    if (IsFile) e.preventDefault();
},false);