Well, you inspired me to some exprimentation so it may be there can be more elegant solution because in all places I tested (Chrome, IE9 in four different modes, node) in both strict and non-strict mode this:
```js
(new Function('return this'))()
```
returns the global object. So both `globalAt:` and `globalExists:` can be more straightforward first getting global object then checking its properties. But I would add it later, as a separate refactoring, when this pullreq is accepted.