this.foo is undefined because in all your examples, this is referring to the global window object. Also, even if you tried obj1.foo, it will still return undefined because the property hasn't been created until the entire expression is evaluated. Try this instead:
var obj1 = {
foo: new Date(),
bar: function() {
return new MyDate( this.foo ); // will work
}
};
It works because by the time you call obj1.bar(), the object will have been created by then; and because you're in a function, the this object will reference the current object.
