How should I replace the key strings in a Javascript key:value hash map (as an object)?

This is what I have so far:

var hashmap = {aaa:foo, bbb:bar};

console.log(before:);

console.log(hashmap);



Object.keys(hashmap).forEach(function(key){

   key = key + xxx;

   console.log(changing:);

   console.log(key);

});



console.log(after:);

console.log(hashmap);

See it running in this jsbin.

The before and after hashmaps are the same, so the forEach seems to be in a different scope. How can I fix it? Perhaps there are better ways of doing this?