Earlier quoted context omitted.
The answer is: that's an expected failure, so you make the error handling explicit by catching the error and taking care of it appropriately (including proceeding to the rest of the page load, naturally). Implicitly handling errors behind JavaScript's loose typing rules is a recipe for disaster.
Explicitly handling errors is almost always a bad idea, no matter what programming language it is. There are very few errors you can reasonably handle, and they must be designed for. It's specific application domains that need different handling strategies: e.g. embedded, device drivers, software that's trying to maintain some very strict invariants. A web page isn't usually one of them. Usually errors should be sent…
Take a look at Common Lisp and Dylan and their respective condition/restart systems. This is how error handling should look like: they let you handle your errors where it makes sense and naturally recover from them if it's possible.