How to remove value from FormData

You cannot do anything other than append items to a FormData object. See the Spec. It would be better if you use a dictionary/object to store all the values you want to add/modify before you actually construct the object.

var data = {};
jQuery.each($('#file')[0].files, function(i, file) {
  data['file-'+i] = file;
});

//modify the object however you want to here

var formData = new FormData();
for (var key in data) {
  formData.append(key, data[key]);
}

I know this thread is old but I just found this : https://developer.mozilla.org/en-US/docs/Web/API/FormData/delete

I'm sur it could help. You can use formData.delete(name) to delete the entry of formData with "name" key.