JQuery :: Copying Object And Leaving Original Intact

The code below is jquery, and uses jquery's extend() [URL] function, but I don't think that the issue has anything to do with that... does it?

$(document).ready(function(){
var obj1 = {
"name": "spud"
,"age":32
}
var obj2 = obj1;
$.extend(obj2, {"location": "UK"});
console.log(obj1);
});

By my reasoning, obj1 shouldn't have location set. But it does. Is the line
var obj2 = obj1;
not making a copy of the original and leaving the original intact? Is it instead making some sort of reference to it? Why is changing the copy having an effect on the original??