while we're here, I'd bind this function iright now so that we don't need to do it in the `addEventListener` call. eg:

```javascript
var recipientsChanged = (function recipientsChanged() { ... }).bind(this);
```

and later

```javascript
this.recipients.on('add', recipientsChanged);
this.recipients.on('remove', recipientsChanged);
```

And this way we have only one function in memory :)