var spread = new GC.Spread.Sheets.Workbook(document.getElementById("ss"));
var sourceSheet = spread.getSheet(0)
var sheet = spread.getSheet(1);
var sourceData = [["Date","Buyer","Type","Amount"],
                 ["01-Jan","Mom","Fuel",74],
                 ["15-Jan","Mom","Food",235],
                 ["17-Jan","Dad","Sports",20],
                 ["21-Jan","Kelly","Books",125]];
sourceSheet.setArray(0, 0, sourceData);
sourceSheet.tables.add('sourceData', 0, 0, 5, 4);
var layout = GC.Spread.Pivot.PivotTableLayoutType.compact;
var theme = GC.Spread.Pivot.PivotTableThemes.medium2;
var options = {showRowHeader: true, showColumnHeader: true};
sheet.pivotTables.add("pivotTable_1", 'sourceData', 1, 1, layout, theme, options);
var pivotTable = sheet.pivotTables.get("pivotTable_1");
pivotTable.addCalcField("calcField", "=Amount*2");
pivotTable.getSourceFields();