WindowBase top

A reference to the topmost window in the window hierarchy.

If this WindowBase is the topmost WindowBase, top will return a reference to the WindowBase itself.

// Add an IFrame to the current window.
IFrameElement myIFrame = new IFrameElement();
window.document.body.elements.add(myIFrame);

// Add an IFrame inside of the other IFrame.
IFrameElement innerIFrame = new IFrameElement();
myIFrame.elements.add(innerIFrame);

print(myIframe.contentWindow.top == window) // 'true'
print(innerIFrame.contentWindow.top == window) // 'true'

print(window.top == window) // 'true'

Source 

@DomName('Window.top')
@DocsEditable()
WindowBase get top => _convertNativeToDart_Window(
    _blink.BlinkWindow.instance.top_Getter_(this));