response.getselectedbutton() is not a function?

I am in school and trying to code a google apps script where I have a function bound to a doc with a custom menu that can create a new doc with the date, subject, and email it to the teacher of said subject. All was going according to plan until I decided to make it so that if I hit cancel instead of OK in one of the parameters I would get the default value of that parameter if I had not hit edit parameters so I could easily only change 1 or 2 things. The function works spotlessly, but now what’s happening is I can’t get the selected button for the alert that asks me if I want to edit parameters.

It just says

"TypeError: response.getSelectedButton is not a function"

and won’t let me run my function. Here’s my code for the function. This has worked fine for me in the past and I’m really not sure why it doesn’t work now.

function Mathdoc() {   var ui = DocumentApp.getUi();   
       var d = new Date();
var s = (d.getDate()) + '/' + (d.getMonth()+1) + '/' + d.getFullYear();
console.log(s);           
                  var response = ui.alert( 'Change parameters?', ui.ButtonSet.YES_NO);
  if (response.getSelectedButton() == ui.Button.YES) {  insert all my other code here}

Is there a glitch or something I’m missing? I’m new to JS and fairly new to web design altogether.

function Mathdoc() {   
  var ui=DocumentApp.getUi();   
  var d = new Date();
  var s = (d.getDate()) + '/' + (d.getMonth()+1) + '/' + d.getFullYear();
  console.log(s);           
  var response=ui.alert( 'Change parameters?', ui.ButtonSet.YES_NO);
  if (response==ui.Button.YES) {  insert all my other code here}