Do not required `config` directly, pass it as a parameter to `ScriptFileStorage` constructor. There is already `isScriptHiddenFn` parameter which comes from `config`, both parameters should be handled consistently.

```js
function ScriptFileStorage(config) {
  this._isHidden = config.isScriptHiddenFn || function() { return false; };
  this._fastLoad = config.fastLoad;
}
```