Setting Content-Transfer-Encoding header using JavaScript

I'm looking to see if the Content-Transfer-Encoding header can be set for a multipart/form-data HTTP request in JavaScript especially for a file upload request.

I came across the Blob API which the File API extends and I can set the Content-Type header like,

var file1 = File(['file1_contents'], 'filename1', {type : 'application/json'});

But I can't seem to set the Content-Transfer-Encoding header.

So, can it be set using JavaScript. If not why not?