console.log((initService('Moscow'))); // возвращает undefined

  function initService(vall) {
    var displaySuggestions = function (predictions, status) {
      if (status != google.maps.places.PlacesServiceStatus.OK) {
        alert(status);
        return;
      }

      console.log(predictions); // возвращает несколько объектов

      return predictions;
    };

    var service = new google.maps.places.AutocompleteService();
    return service.getQueryPredictions({ input: vall }, displaySuggestions);
  }