How to check if input file is empty in jQuery

Just check the length of files property, which is a FileList object contained on the input element

if( document.getElementById("videoUploadFile").files.length == 0 ){
    console.log("no files selected");
}

Here is the jQuery version of it:

if ($('#videoUploadFile').get(0).files.length === 0) {
    console.log("No files selected.");
}

To check whether the input file is empty or not by using the file length property, index should be specified like the following:

var vidFileLength = $("#videoUploadFile")[0].files.length;
if(vidFileLength === 0){
    alert("No file selected.");
}

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');
  }

}