how to create a custom function for use in a .xlsx in onlyoffice

Question

I want to edit a .xlsx document in Onlyoffice, and in a cell, write "=TOLETTER(E1)" where TOLETTER is a function that I define.

I know how to do that in Excel (with a VBA Script).

I have done it in Google Sheet (with JS).

I have not found documentation or an example for Onlyoffice. Onlyoffice macros or plugins are closures and I lack the info how to define/export a function that will be visible from the cell.

Answer 1

Currently Onlyoffice doesn't support user defined functions, only macros as you mentioned, using JavaScript and the Document Builder API.