Google forms duplicates sections when running Google Apps Script multiple times - google-apps-script

Question

I've got a code in Google Apps Script to automatically populate a Google Form. It works perfectly, but there's one big problem. When I run the script multiple times, the Forms copies itself. So, instead of overwriting the previous run, it adds a whole new (identical) Form. For example: after running the code one time, it shows 4 sections. But when I run it two times, it shows 8 sections, and so on.
Does anybody know how to solve this?
Here's the used code:
function rosterMaker() {
//spreadsheet id of the rosters
var SHEET_ID = FormApp.getActiveForm().getDestinationId();
var ss = SpreadsheetApp.openById(SHEET_ID)
var form = FormApp.getActiveForm();
var sheets = ss.getSheets().filter(function(sheet) {return sheet.getName().match(/Roster/gi);});
//add multiple choice item
var classSelect = form.addMultipleChoiceItem();
classSelect.setTitle('Choose a class');
var classChoices = [];
for(var i = 0; i < sheets.length; i++) {
var className = sheets[i].getName();
var classSection = form.addPageBreakItem()
.setTitle(className)
.setGoToPage(FormApp.PageNavigationType.SUBMIT);
var students = getStudents(sheets[i]);
var studentSelect = form.addCheckboxItem()
.setTitle(className + 'absent')
.setHelpText('Select the students who are absent from this class');
var studentChoices = [];
for(var j = 0; j < students.length; j++) {
studentChoices.push(studentSelect.createChoice(students[j]));
}
studentSelect.setChoices(studentChoices);
classChoices.push(classSelect.createChoice(className, classSection));
}
classSelect.setChoices(classChoices);
}
function getStudents(sheet) {
var studentValues = sheet.getDataRange().getValues();
var students = [];
for(var i = 1; i < studentValues.length; i++) {
students.push(studentValues[i].join(' '));
}
return students;
}

Answer 1

What you need to do is remove all the items you populated in your form before populating it again. Best place to add it on should be before adding anything to the form.
Based on your script, you can add it after var form = FormApp.getActiveForm();
See my sample code below on how it works.
var formID = <FORM_ID>;
var fData = FormApp.openById(formID);
function clearForm(){
// function that clears all items in your form
var items = fData.getItems();
// always delete while there is remaining item
while(items.length > 0){
fData.deleteItem(items.pop());
}
}
function populateForm() {
// call clearForm to prevent duplicating populated questions
clearForm();
// section to populate your form
// ....
}
If you have any issues/problems on making the code work, feel free to comment below.