Copy An Object?

If I create an object with the following:

var ob1 = new objMyDefinedObject();

then I assign it to a new variable.

var ob2 = ob1

I know that this isn't coping the object into a new variable, its just
another reference to the SAME object unlike

var a = 20;
var b= a;

Which creates a copy of the variable "a" and stores it in variable "b".

How can I copy my above object into a new variable rather than
reference the same object ? What I want to do is create the object, do
a load of property changes, then copy the object into a new variable
and do a load more property changes.