`script_name` should refer to either:

1. function name, e.g.

`GOVUK.someNamespace.MyConstructor`

2. name of a variable containing an object literal (singleton), e.g. assuming we already had this defined somewhere:

```
GOVUK.someNamespace.myThingummy = {
  init: ...
}
```

then pass in

`GOVUK.someNamespace.myThingummy`

so maybe `script_name` should be renamed to `constructor_or_singleton_name`