You can use:
element1.isEqualNode(element2);
In your specific example:
var divs = $(".a");
if ( divs.get(0).isEqualNode(divs.get(1)) ) alert("Same");
The DOM Level 3 Core Spec has all the details. Essentially this returns true of the two nodes have matching attributes, descendents, and the descendents’ attributes.
There’s a similar .isSameNode() that returns true only if both elements are the same node. In your example, these are not the same nodes, but they are equal nodes.