var newDeliverydate = "27.8.2018";
var convertDate = newDeliverydate;
var newConvertDate = newDeliverydate.split(".").reverse().join("/");

var d = new Date(newConvertDate);
var newDeliveryDateIso = d.toISOString();


nestaci len bez toho var d:

var newDeliverydate = "27.8.2018";
var newConvertDate = newDeliverydate.split(".").reverse().join("/");

var newDeliveryDateIso = newconvertDate.toISOString();