I know I'm late to the party but I thought I'd add what I ended up using for this - which is to simply check if the file upload input does not contain a truthy value with the not operator & JQuery like so:
if (!$('#videoUploadFile').val()) {
alert('Please Upload File');
}
Note that if this is in a form, you may also want to wrap it with the following handler to prevent the form from submitting:
$(document).on("click", ":submit", function (e) {
if (!$('#videoUploadFile').val()) {
e.preventDefault();
alert('Please Upload File');
}
}