observer.js

// setting up an observer

var query = SC.Query.local(MyApp.Record);
var data = MyApp.store.find(query);

var f = function(data) {
  if (data.get('status') & SC.Record.READY) {
    // data is ready
    return YES;
  }
  return NO; // optional, if nothing is returned then it shouldn't be removed
}

data.addFiniteObserver('status', this, f);