message-reducer.ts

 case EMessageActions.AddMessage:
      const channelId = action.payload[0];
      const newMsg = action.payload[1];
      const entity = state.entities[channelId];

      const newMsgArray = [
          ...entity.messages,
          newMsg
      ];

      // Creates new entity with the new message, or updates an existing entity and appends message
      return messageAdapter.upsertOne({
          ...entity,
          messages: newMsgArray
      }, state);