If you are using jQuery, you can get the size of the window or document using jQuery methods:

$(window).height();   // returns height of browser viewport
$(document).height(); // returns height of HTML document (same as pageHeight in screenshot)
$(window).width();   // returns width of browser viewport
$(document).width(); // returns width of HTML document (same as pageWidth in screenshot)

For screen size you can use the screen object in the following way:

screen.height;
screen.width;