Understand variables, like n.serviceWorker

When code has `navigator.serviceWorker` it will return error (is Ok)

```
22: navigator.serviceWorker
^^^^^^^^^^^^^ `ServiceWorker` is not supported in IE 11, Edge 15 and Safari 8 😢
```

while when used variables like

```
var n = navigator;
n.serviceWorker.register(...);

it doesn't return error while is expected to have (not Ok).