Google slides - change font for every slide using apps script

gistfile1.txt

//script adapted by @dsottimano 
//original from: https://stackoverflow.com/questions/52569689/clear-text-formatting-in-slides-using-apps-script
//credit to https://stackoverflow.com/users/7108653/tanaike


function onOpen() {
  SlidesApp.getUi() 
      .createMenu('Custom Menu')
      .addItem('Change Master Font', 'changeFont')
      .addToUi();
}


function getFont() {
  var ui = SlidesApp.getUi();
  
  var result = ui.prompt(
    'Replace all fonts',
    'Please enter the exact name of the font you want to use on every slide:',
    ui.ButtonSet.OK_CANCEL);
 
  if (result.getSelectedButton() == ui.Button.OK) {
    return result.getResponseText();
    
  } else {
    return false
  }
}


function toDefault(text,font) {
  if (text.getRange(0,1).asString().charCodeAt(0) != 10) {
    var style = text.getTextStyle();
    return style.setFontFamily(font);
  }
  return null;
}

function changeFont() {
  var font = getFont(); 
  var slideDeck = SlidesApp.getActivePresentation();
  var pageElements = [];
  var slide = slideDeck.getSlides().forEach(function(s) {
  pageElements.push(s.getPageElements());
  }) 

  pageElements = pageElements.flat(Infinity);
  pageElements.forEach(function(e) {
    if (e.getPageElementType() == "SHAPE") {
      var text = e.asShape().getText(); 
      toDefault(text,font);
    } else if (e.getPageElementType() == "TABLE") {
      var table = e.asTable();
      
      for (var row = 0; row < table.getNumRows(); row++) {
        for (var col = 0; col < table.getNumColumns(); col++) {
          var text = table.getCell(row, col).getText();
          toDefault(text,font);
        }
      }
    }
  });
}


Array.prototype.flat || Object.defineProperty(Array.prototype, "flat", {
    configurable: !0,
    value: function r() {
        var t = isNaN(arguments[0]) ? 1 : Number(arguments[0]);
        return t ? Array.prototype.reduce.call(this, function (a, e) {
            return Array.isArray(e) ? a.push.apply(a, r.call(e, t - 1)) : a.push(e), a
        }, []) : Array.prototype.slice.call(this)
    },
    writable: !0
}), Array.prototype.flatMap || Object.defineProperty(Array.prototype, "flatMap", {
    configurable: !0,
    value: function (r) {
        return Array.prototype.map.apply(this, arguments).flat()
    },
    writable: !0
})

see adjusted code (error handling for merged cells)> https://gist.github.com/tpetrzilkaCD/c2c990138d8924e22398da826cbaa910