Print only the user Created fields in Sharepoint using JavaScript

<script>

$(document).ready(function{

var listTitle="TestList";
var viewname="Myview";
retrieveFieldsOfListView(listTitle,viewName);

});

function retrieveFieldsOfListView(listTitle,viewName){

   var context = new SP.ClientContext.get_current();
   var web = context.get_web();
   var list = web.get_lists().getByTitle(listTitle);
   var listFields = list.get_fields();
   context.load(listFields);
   context.executeQueryAsync(printFieldNames,onError);


   function printFieldNames() {
      var e = listFields.getEnumerator();
     while (e.moveNext()) {
  var field = e.get_current();
  var schema = field.get_schemaXml();
  if (/SourceID="http/i.test(schema)){
      alert("custom field found:" + field.get_title());
  }
}

   function onError(sender,args)
   {
      alert(args.get_message());
   }

    }

</script>