Kendo TreeView should return a promise. When using treeview and setting loadOnDemand: true when you call expand on a node that has not been loaded there's no way to know when the loading has completed. Returning a promise will allow the developer to know when the expansion has completed.
Hello,
You can use the expand event as per your requirements: https://docs.telerik.com/kendo-ui/api/javascript/ui/treeview/events/expand.
Regards,
Ianko
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