How to replace/name keys in a Javascript key:value object?

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?

Answer

It has nothing to do with scope. key is just a local variable, it’s not an alias for the actual object key, so assigning it doesn’t change the object.

Object.keys(hashmap).forEach(function(key) {
  var newkey = key + "xxx";
  hashmap[newkey] = hashmap[key];
  delete hashmap[key];
});