That's right it's not a Window object it's a jQuery object, it should return false.

So why does jQuery(window).is(window) return false as well? You are basically saying once the window is wrapped, it becomes something new. That's just wrong.

jQuery(window).is(window) returns false because window falls through the function, node, and string checks in the code enabling .is: https://github.com/jquery/jquery/blob/10399ddcf8a239acc27bdec9231b996b178224d3/src/traversing/findFilter.js#L11-L38. This would also be true of other non-DOM objects (e.g., jQuery([ Math ]).is( Math ) === false).

jQuery collections containing non-node members (or even non-''element'' members, in many cases) don't always behave well, and .is is an area where we care about performance. But I wouldn't object to a small fix, if someone is interested in doing the legwork.

jQuery.isWindow seems pretty well documented to examine its object and I don't know why it would strip off wrappers or try to look into the contents of the object it's given to find a window. http://api.jquery.com/jQuery.isWindow/

For jQuery(window).is(window) the docs say window isn't a valid input, so at most that would be a feature request. It's easy to do jQuery.isWindow(jQuery(window)[0]) http://api.jquery.com/is/

jQuery(document).is(document) returns true on the other hand. Well, I obviously don't get the philosophy of it. Anyway, thanks for the explanations everyone, I will just "adjust" this for my own then.