[jQuery] a problem with $.each() function

[jQuery] a problem with $.each() function


when i write
$(document).ready(function(){
    $.each(document,function(k,v){
        document.writeln(k+"===="+v+"<br />);
    });
});
it works ,but when i change the document to window,as follows
$(document).ready(function(){
    $.each(window,function(k,v){
        document.writeln(k+"===="+v+"<br />);
    });
});
nothing output,why?
thank u all!