Hi Jmarshall,
We tried to build a sample to you, but it looks use CustomViewModel is not a good solution.
We succeed to pass CustomViewModel to client side, but all the value get parsed when page init, and in JavaScript code it cannot get any value from the CustomViewModel. So we cannot pass anything back via ajaxCallAction.
So I think you should want to use JsonString instead of the CustomViewModel, you can pass that back via ajaxCallAction, and then return the changed result to client side, after that call our client side API to modify the result in client side.
And you can modify in server side also, just in the server side event modify the “map”. And then redraw map in client side, please notice the client cache should get clear orelse you won’t see the change.
Regards,
Ethan