Window: parent property

The 
Window.parent property is a reference to the parent
of the current window or subframe.
If a window does not have a parent, its 
parent property is a reference to
itself.
When a window is loaded in an iframe, object, or
frame, its parent is the window with the element embedding the
window.
Value
A 
Window or iframe object.
Examples
if (window.parent !== window.top) {
  // We're deeper than one down
}
Specifications
Browser compatibility
See also
window.frameElement returns the specific element (such as
<iframe>) the 
window is embedded into.
window.top returns a reference to the top-level window.