In an ordinary browser window, the default scope of JavaScript code is
the window, so this refers to the window object. The line
var window = this;
has no purpose except to allow the YUI Compressor to change the
variable name to save space. Thus, code like this (for example):
var window = this;
window.scrollTo(0, 120);
can be reduced to
var A = this;
A.scrollTo(0, 120);
Then, A is a reference to window, and you don't need to spell out the
entire word "window" each time you want to refer to it.
Hopefully that was clear.
~spicyj