origin

A string representing the current origin of the frame, serialized according to RFC 6454. This may be different from the URL. For instance, if the frame is a child window opened to about:blank, then frame.origin will return the parent frame's origin, while frame.url will return the empty string. Pages without a scheme/host/port triple origin will have the serialized origin of "null" (that is, the string containing the letters n, u, l, l).