GoogleCalendarHoliday.gs

// Set the ID of the team calendar to add events to. You can find the calendar's
// ID on the settings page.
var TEAM_CALENDAR_ID = '*****@group.calendar.google.com';
// Set the email address of the Google Group that contains everyone in the team.
// Ensure the group has less than 500 members to avoid timeouts.
var GROUP_EMAIL = '***@****.com';
var MONTHS_IN_ADVANCE = 1;
// If your imported the holiday calendars past their ID's here
var CALENDER_IDS = [
  "****@import.calendar.google.com",
  "****@group.v.calendar.google.com",
  "****@group.v.calendar.google.com",
]
var gxCalendar = CalendarApp.getCalendarById(TEAM_CALENDAR_ID);

/**
 * Setup the script to run automatically every hour.
 */
function setup() {
  var triggers = ScriptApp.getProjectTriggers();
  if (triggers.length > 0) {
    throw new Error('Triggers are already setup.');
  }
  ScriptApp.newTrigger('sync').timeBased().everyHours(1).create();
  // Run the first sync immediately.
  sync();
}

/**
 * Look through the group members' public calendars and add any
 * 'vacation' or 'out of office' events to the team calendar.
 */
function sync() {
  // Define the calendar event date range to search.
  var today = new Date();
  var maxDate = new Date();
  maxDate.setMonth(maxDate.getMonth() + MONTHS_IN_ADVANCE);

  // Determine the time the the script was last run.
  var lastRun = PropertiesService.getScriptProperties().getProperty('lastRun');
  lastRun = lastRun ? new Date(lastRun) : null;

  // Get all events of calenadrs
    for (var i = 0, clen = CALENDER_IDS.length; i < clen; i++) {
     var cal = CalendarApp.getCalendarById(CALENDER_IDS[i]);
     var events = cal.getEvents(today, maxDate);
     for(var i=0; i<events.length;i++) {
       var event = events[i];
       importEvent(cal.getName(), event);
     }
   }
  PropertiesService.getScriptProperties().setProperty('lastRun', today);
}

/**
 * Imports the given event from the user's calendar into the shared team
 * calendar.
 * @param {string} username The team member that is attending the event.
 * @param {Calendar.Event} event The event to import.
 */
function importEvent(calendarname, event) {
  console.log('Importing: %s', event.summary);
  try {
    gxCalendar.createAllDayEvent('[' + calendarname + '] ' + ' -> ' + event.getTitle(), event.getAllDayStartDate(), event.getAllDayEndDate());
  } catch (e) {
    console.error('Error attempting to import event: %s. Skipping.',
        e.toString());
  }
}