Objects are passed around by reference. They are never copied:

var x = stooge;
x.nickname = 'Curly';
var nick = stooge.nickname;
    // nick is 'Curly' because x and stooge
    // are references to the same object

var a = {}, b = {}, c = {};
    // a, b, and c each refer to a
    // different empty object
a = b = c = {};
    // a, b, and c all refer to
    // the same empty object