[codewars] String Reordering

The input will be an array of dictionaries.

Return the values as a string-seperated sentence in the order of their keys' integer equivalent (increasing order).

The keys are not reoccurring and their range is -999 < key < 999. The dictionaries' keys & values will always be strings and will always not be empty.

Example

Input:
List = [
        {'4': 'dog' }, {'2': 'took'}, {'3': 'his'},
        {'-2': 'Vatsan'}, {'5': 'for'}, {'6': 'a'}, {'12': 'spin'}
       ]

Output:
'Vatsan took his dog for a spin'

My Answer

function sentence(List) {
  return List.sort((curr, next) => Object.keys(curr)[0] - Object.keys(next)[0]).map(item => item[Object.keys(item)[0]]).join(' ');
}