Hi,
Sorry for not replying – the email notification on my site broke after an update and I didn’t catch your question.
You cannot add an item to a document library using spjs.utility.addItem() because you have to add a document and not just metadata. It is possible to create a document from text using code, but not using that function.
If you haven’t moved on you can try to explain what you are trying to achieve and I’ll see if I can help you on the way.
Alexander