leeq3000
http://www.devthought.com/2012/01/18/an-object-is-not-a-hash/
http://www.2ality.com/2012/01/objects-as-maps.html
http://ryanmorr.com/true-hash-maps-in-javascript/
Until then, or even after, you should look to bare objects for all your basic hash map needs.
