Do you think this would be clearer if the config values were pulled out and assigned to instance properties? Something like this:

```javascript
this.config = config;
this.is_submitted_url = config.is_submitted_url;
this.quiz_id = config.quiz_id;
this.redirect_url = config.redirect_url;
```
Then anywhere in the code where you were referencing `this.config` you replace it with a reference to the instance property. The advantage of that approach is that it's clear just by reading the code what instance properties are expected to be there. The comment helps with that, but even then, it's not as clear as it could be. Just a suggestion.