The approach to use the edit event is correct. The alert will not be triggered because the event arguments are different:
- instead of dataItem you should use model.
- instead of mode you should use the model isNew method.
- instead of form you should use container.
It is also possible to use visible or invisible binding in the popup template in order to show or hide the editors automatically based on the value e.g.
@Html.EditorFor(m => m.Username)
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