Issues when document.body is null? #75
Description
In another round of mysterious errors...
I've seen some cases where it looks like the mutationobserver is trying to be set up before the DOM is ready.
I'm seeing the error with this line:
this._observer.observe(this._document.body, { attributes: true, subtree: true, childList: true });
Errors returned: "TypeError: Argument 1 of MutationObserver.observe is not an object."
It's happened in FF 55,56 on Linux, Mac and Windows as well as IE 11 and Edge.
It looks like the readyState checking all makes sense, so I'm not sure what's the cause yet.