this function gets called once the user drops the file onto the div
function handleFileSelect(evt) {
        evt.stopPropagation();
        evt.preventDefault();

        // Get the FileList object that contains the list of files that were dropped
        var files = evt.dataTransfer.files;

        // this UI is only built for a single file so just dump the first one
        dumpFile(files[0]);
    }