Keeping track of doc's words count in google apps script

Question

I'm writing a Google Docs Add-on and would like to keep track of word count in the extension whenever user adds/deletes new word.

My initial approach is:

in Code.gs:

function getWordCount() {
  var st = DocumentApp.getActiveDocument().getBody().getText().replace(/\n/g, ' ') + ' ';
    st = st.split(/\s* \s*/).length;
    return st - 1;
}

in Sidebar.html:

var docCount = 0;
function updateWordCount(data) {
   if(data) {
     docCount = data;
   }
   google.script.run.withSuccessHandler(updateWordCount).getWordCount();
}

But it seems very 90th... is there any way to push data from google apps script to client side? I know about Google Realtime API but it doesn't work in apps script for Google Docs.

Regards