Word Web Addin: Event handler for text changed

Question

Hello all,

I am developing a word web add-in for Office 2019. I suppose that I have just understood fundamentals for web add-in. Would like to hook text changed event handler on a document, but I couldn't figure out how it can be do. I googled so much, however I couldn't find out any info even a hint.
I also asked it on stackoverflow. A guy answered it doesn't support at this time, and he also said me to post a question here, and encouraged me to request to add this feature.
If it is correct that he said, I want to request to improve Office JavaScript API for future.