river.core.modelis riverjs core module. It's response for compare old value and new value. all the
scopeobject is instance of it.
once you call
scope.apply, the model compare system will be startup to find which value has been changed.Once find any changes happend, model will sync view and module scope.
scopechanged , the
callbackwill be trigger, the newvalue and oldvalue will be passed in as arguments