Validate EmberJS TextField on the fly?

I need to validate a form textfield that's bound to a property of a model using EmberJS. I want the user to only be able to type valid, positive numbers.

I know of jQuery.isNumber(), but I don't know how to wire it to the field. I tried writing explicit getter/setter functions on the model's property using Ember.computed(...), but it didn't work.

Is there something similar to WinForms onChanging() event that I can hook up to?