record_loading.js

var record = MyApp.store.find(MyApp.Record, 1);

record.addObserver('status', this, function() {
  if (record.get('status') === SC.Record.READY_CLEAN) {
    record.removeObserver('status', this, arguments.callee);
    
    // code here
  }
});

// if we want the observer called even if the record is already loaded
if (record.get('status') === SC.Record.READY_CLEAN) record.notifyPropertyChange('status');