Office JS Add-In: Get excel file with Office JS on iPad

Question

I am currently building an office add-in that should work for word, powerpoint and excel that takes the word/powerpoint document or excel sheet as a binary file using Office JS and transfers it to a third party site with the add-in.

With word and powerpoint this works perfectly everywhere. Unfortunately there is a slight problem with excel on iPads.

The function I'm using to get the file via Office JS is Office.context.document.getFileAsync(...). If you look at the API reference below, this function is supported everywhere except for excel on the iPad. I have no clue as to why this is and I was not able to find any alternative to using this function to get the excel file.

see also: https://learn.microsoft.com/en-us/javascript/api/office/office.document?view=excel-js-1.17#office-office-document-getfileasync-member(1)

Is there any other way to get to the file, than to use this function?

Thanks in advance for your help. Simon