How to update the model via javascript?

I understand we can use [
] and {{}} bindings to link data to the model - but how do I update the model if I want to change things via a component that does not work with these bindings?

I have tried to push to the path, but that doesn’t seem to update the server side.

Is there a way to do this without having to write an async handler and RPC from javascript back to the server?