Email Notifications from Date in Spreadsheet

function emailReminder() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var leases = ss.getSheetByName("Leases").getDataRange().getValues();
  var emails = ss.getSheetByName("Emails").getDataRange().getValues();
  

  var notificationWindows = {}
  notificationWindows[addMonths(new Date(),6)] = makeNotifications(emails, "Six Months");
  notificationWindows[addMonths(new Date(),3)] = makeNotifications(emails, "Three Months");
  notificationWindows[addMonths(new Date(),1)] = makeNotifications(emails, "One Month");
  notificationWindows[addWeeks(new Date(),2)] = makeNotifications(emails, "Two Weeks");
  notificationWindows[addWeeks(new Date(),1)] = makeNotifications(emails, "One Week");


for(var i in leases){     
  if(leases[i][1] in notificationWindows){
      notificationWindows[leases[i][1]](leases[i][0]);
    }
  }
}


function addMonths(date, months) {
  date.setMonth(date.getMonth() + months);
  date.setHours(0,0,0,0);
  return date;
}

function addWeeks(date, weeks){
  date.setDate(date.getDate() + (weeks * 7));
  date.setHours(0,0,0,0);
  return date;
}


function makeNotifications(emails, timeToExpire){   
   return function(property){
     for(var i in emails){
       var notification = "The lease for " + property + " is set to expire in " + timeToExpire;
       MailApp.sendEmail(emails[i][0], notification, notification);
     }
   }
}