Script to add events on google calendar using a google spreadsheet

calendarSync.js

function calendarsync() {
    var spreadsheet = SpreadsheetApp.getActiveSheet();
    var calendarId = spreadsheet.getRange("C3").getValue();
    var eventCal = CalendarApp.getCalendarById(calendarId);
    var signups = spreadsheet.getRange("A38:D51").getValues();
    for (x = 0; x < signups.length; x++) {
        var shift = signups[x];
        var nameEvent = shift[0]
        var startEvent = shift[1];
        var endEvent = shift[2];
        var notes = shift[3];
        eventCal.createEvent(nameEvent, startEvent, endEvent, {
            description: notes
        });
    }
}
function onOpen() {
    var ui = SpreadsheetApp.getUi();
    ui.createMenu('Sincronizza')
        .addItem('Google Calendar', 'calendarsync')
        .addSeparator()
        .addSubMenu(ui.createMenu('Cancella')
            .addItem('Cancella gli eventi', 'clearCalendar'))
        .addToUi();
}
function clearCalendar() {
    // undeclared function
}