code: function forEachProperty(map, callback) {
          var result;
          for (var key in map) {
              if (result = callback(map[key], key))
                  break;
          }
          return result;
      }
docs: Enumerates the properties of a Map<T>, invoking a callback and returning the first truthy result.
  
  @param map A map for which properties should be enumerated.
  @param callback A callback to invoke for each property.