I use filepicker.io to handle upload. But I want the user to provide additional data related to the uploaded file, so basically I would need to add to the modal some comboboxes and text inputs. Is it possible by using the widget approach with the filepicker.constructWidget call?
I'm afraid it's not possible, constructWidget only accepts addition options listed here https://www.filepicker.com/documentation/file_ingestion/widgets/programming?v=v1 and a type which can be 'filepicker' or 'filepicker-dragdrop'. You would need to try a different approach i.e. add the text inputs after the modal is called and files uploaded.