function getAnyKey(obj) {
  for (const key in obj) {
    return key;
  }
}
Returns one key from the object map, if any exists.
For map literals the returned key will be the first one in most of the
browsers (a know exception is Konqueror).
@param {?Object} obj The object to pick a key from.
@return {string|undefined} The key or undefined if the object is empty.