Window: outerWidth property
Window.outerWidth read-only property returns the width of the outside of the browser window. It represents the width of the whole browser window including sidebar (if expanded), window chrome and window resizing borders/handles.
Notes
To change the size of a window, see window.resizeBy() and window.resizeTo().
To get the inner width of a window, i.e. the width of the page being displayed, see window.innerWidth.