code: function mapObject(f, obj) {
    return reduce(function mapObjectExecute_(sum, v) {
      sum[v] = f(obj[v], v);
      return sum;
    }, objectKeys(obj), {});
  }
docs: Map a function over an object.
  @param {object} obj The object.
  @param {function} f The function.
  @return {object} The resulting object.