Swap the names/properties in a JavaScript object

Question

Is there a more elegant way to do this in JavaScript?

function swapKey(obj, oldKey, newKey) {
 if (obj[oldKey]) {
 obj[newKey] = obj[oldKey];
 delete obj[oldKey];
 }
 return obj;
}

(I understand that it mutates the original object and is not functional and makes the returning of obj somewhat redundant and that's okay for this particular question.)

Answer 1

So the idea is to change the key of a given pair. Few issues:

• Your code doesn't guard against existing keys. If my newKey is an already existing key, it would overwrite the existing value, and delete the old key.

• Like mentioned, mutation. Unless you're fully aware of the things that reference the object or have mechanisms in place to capture suddenly missing properties, you shouldn't mutate in-place. In the case above, if you accidentally delete an existing key another piece of code expects to exist, this will cause unexpected breakage.

• Your condition will return true for prototype members. Always do a hasOwnProperty check to ensure that you're only checking the instance, not the prototype.

• Guy: Great points - thanks @Joseph the Dreamer. So there's no in-place way to rename the key of a key/value pair then?
• Joseph: @Guy There is, and you just did it. Just be wary about the consequences.