Update Fields with officejs after changing DocumentProperty

Hi all,

I'm looking for some help and I can't find the answer online.

I'm building a Word Add-in with officejs 1.3. 
On this Add-in the user fills-out a form. With the given data I override or add these to CustomDocumentProperties.

The 'Fields' on the document is not updatet and keep showing the old data. Even after closing and opening the document. Only when I right-click on the 'Field' and choose for 'Update Field' the updatet value is shown.

I can't use Macro's because it has to work on a Mac as well.

In VSTO, we can easily update fields of a Word document using c# code:

_wordApplication.ActiveDocument.Fields.Update();

But how do I manage this with officejs?

Thanks for helping me out!

Jeffrey