Hi Hartono,
Thanks for contacting Syncfusion support.
In the shared KB documentation, we have provided response for “The type or name 'JavaScript' does not exist in the namespace 'Syncfusion' - are you missing an assembly reference? " issue. The mentioned issue occurs when the Syncfusion assemblies are not referred properly in your application. If issue still persists even after referring the Syncfusion assemblies, then it might occur when the Syncfusion namespace references were not added in web.config file in your application. So we request you to specify the “Syncfusion.JavaScript.Web” namespaces in web.config as shown in the screenshot in your application to rectify the mentioned issue at your end.
We have prepared a sample and it can be downloaded from the below location,
If the issue still persists, then revert the shared sample with issue reproducible steps to validate the mentioned issue at our end.
Regards,
Yuvaraj D.