I think the cleaner way to write this block is:

```
var results_types = []
if (!_util.getLocalData('courses')) {
  result_types.push('courses');
}
if (!_util.getLocalData('friends')) {
  result_types.push('friends');
}
result_types.join(',');
```

This way you won't end up with a trailing empty string entry when you do the `split()`.

Also, nit: rename `result_types` to `resultTypes`.