Asynchronously(one after the other) execute bits of code

async

this.renderUI = function(res) {
      var connected = (res.user != null && res.user.isConnected);
      var contactsData = [];
      if(connected) {
        $j('#jive-modal-invite').trigger('close');
        contactsData['contacts'] = gigya.socialize.getContacts({callback: function(response){ // How can I async js this line such that only when this returns should alert be called?
          contactsData['contacts'] = response;
        }});
        alert(contactsData); // returns null
      }
    };

// Executing the code will return 'undefined' for contactsData.

gigya.socialize.getContacts({callback: function(response){
contactsData['contacts'] = response;
},
gigya.socialize.getContacts.contactsData = contactsData;
});

gigya.socialize.getContacts({callback: function(response){
contactsData['contacts'] = response;
}
},
gigya.socialize.getContacts.contactsData = contactsData;
);