Google Apps Script – Duplicate Check for Google Contacts

This piece of code retrieves the contacts of the group first and checks whether an e-mail address corresponds to one of the sheet entries:

Code

function bulk_cdb_one_way_sync(){
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var cdb = ss.getSheetByName("Bulk_CDB").getDataRange().getValues();
  var group = ContactsApp.getContactGroup("Preview List");
  var groupContacts = ContactsApp.getContactGroup("Preview List").getContacts();

  for (var x=1, xLen=cdb.length; x<xLen; x++) {
    var aContact = [];
    aContact.push(cdb[x][0], cdb[x][1], cdb[x][2], cdb[x][6]);
    var c = 0;  
    if(groupContacts.length > 0) {
      c =+ 1, u = 0;
      for(var i in groupContacts) {
        var emails = groupContacts[i].getEmails();
        for(var j in emails) {
          if(emails[j].getAddress() == aContact[2]) {
            u += 1;
            continue;
          }
        }
      }
    }

    if(c === 0 || u == "undefined" || u === 0) {          
      var c = ContactsApp.createContact("There","Painter", aContact[2]);
        c.addCustomField("Metro 1", aContact[1]);
        c.addCustomField("Status", aContact[0]);
        c.addPhone(ContactsApp.Field.WORK_PHONE, aContact[3]);
        c.addToGroup(group);
    }  
  }
}

Explained

The groupContacts retrieves all available contacts in the group. The x=1 makes sure to skip the header and the array (aContact) is created for easy access. If the group has no entries, then c will remain 0 and the new contacts will be added. Then the script will itterate over the contacts and over the e-mails present. If a match is found, u will be > 0 and no contact is added.

Remark

Make sure the data you about to add contains no duplicates.....