Using ClearScriptConsole, I find:
-> typeof host.Where
That is, a method on a host object is not reported to be a "function", even though it can be called with (). Contrast this with the situation in IE or Chrome's debug consoles:
I encountered this when trying to use JSON.stringify on a tree of objects, e.g. a JS array of host objects. I need to control how the host object is serialised, so (in accordance with how JSON.stringify works) I implemented toJSON as a method on my host class.
But JSON.stringify uses typeof to check whether toJSON is a function. It gets the answer "object", so it does not call it.