How to pass a parameter to PdfAction.JavaScript(jscode, stamper.Writer)

           // test

            AcroFields form = stamper.AcroFields;

            var fields = form.Fields;

            var fieldKeys = form.Fields.Keys;

            foreach (string fieldKey in fieldKeys)

            {

                if (fieldKey.Contains("timeholder"))

                {                   

                    float[] fieldPos = form.GetFieldPositions(fieldKey);

                    var fieldLlx = fieldPos[1];

                    var fieldLly = fieldPos[2];

                    var fieldUrx = fieldPos[3];

                    var fieldUry = fieldPos[4];

                    Rectangle recTime = new Rectangle(fieldLlx, fieldLly, fieldUrx, fieldUry);

                    PushbuttonField btnTime = new PushbuttonField(stamper.Writer, recTime, "post");

                    PdfAnnotation timeButton = btnTime.Field;

                    timeButton.Action = PdfAction.JavaScript(

                      "var date = this.getField(\"03 Time timeholder\"); date.value = new Date().toLocaleTimeString();", stamper.Writer

                    );

                    stamper.AddAnnotation(timeButton, 1);

               }

          }

          stamper.Close();

The above codes work properly, my question is how to pass fieldKey to PdfAction.JavaScript() to replace "03 Time timeholder"

Thanks a lots.

Tony