Add global error event handler

As far as I can tell, there is no way to set the global event handler for [window.onerror](https://developer.mozilla.org/en-US/docs/Web/API/GlobalEventHandlers/onerror). The following code does nothing:
```
window.onerror = function() {
console.log('Global Error!', arguments.length);
return true;
};
throw new Error('TEST');
```
Would it be possible to add this functionality?