var customFormatterTest = {};
customFormatterTest.prototype = GC.Spread.Formatter.FormatterBase;
customFormatterTest.format = function (obj, conditionalForeColor) {
    conditionalForeColor.value = "blue";
    return "My format result : " + obj.toString();
};
customFormatterTest.parse = function (str) {
    if (!str) {
        return "";
    }
    return str;
}
activeSheet.getCell(1, 0).formatter(customFormatterTest);
activeSheet.getCell(1, 0).value("Test");