We have an order form that has a series of fields related to a chosen PDF for printing - for instance the width and height of the PDF, as well as what kind of product it's supposed to be printed on, and so forth. A user can click on a "choose file" button to select a file from their computer, or drag a file (or multiple files) from their computer's file explorer onto the page to upload them that way.
1) When dragging a file or series of files onto the order form, those files are added to a hidden form (#dropform) on the page, along with info on all the other files already on the page, including files selected via the "choose files" button, the quantity, kind of product, and other info from each line
2) The #dropform is submitted to another PHP file that uploads the dropped files and handles the data via Ajax xhr. The files and line data are all stored in arrays that are set in this php file as $_SESSION variables. The order form page then displays these items and selections on the order form successfully in all browsers except for Internet Explorer (we need it working in at least IE 11).
3) We've narrowed it down to being something wrong with the handling of the dragged files, as none of the drag/dropped files are getting to the PHP file that handles the uploads, but looking at the #dropform info on the page in IE11, the drag/dropped files are there as they should be but aren't when the form is submitted, so somehow they're being lost.
4) IE support for formData is limited but according to Mozilla and other sources IE 11 supports [login to view URL] and the formData constructor, which are the only two things used in our code for formData.
5) We have tried setting different headers for IE found in online searches, adding timeouts to see if it was a timing related issue, and rewriting the Ajax script in multiple ways but each has failed to work in IE even though it works in other browsers. The code isn't throwing errors either which has made this very difficult to figure out.