这是使用javascript 传播语法的更简洁的方法：

const initialState = {
    photos: [],
    selectedPhoto:{},
    photosTeamId:'',
    photosProjectId:''
};

case actionTypes.PHOTOS_UPDATE:
            return {
                ...state,
                photos: [...state.photos, ...actions.data.photos],
                photosTeamId: action.data.photosTeamId,
                photosProjectId: action.data.photosProjectId
            }

case actionTypes.PHOTOS_UPDATE:
  return {
    ...state,
    photos: state.photos.concat(action.data.photos),
    photosTeamId: action.data.photosTeamId,
    photosProjectId: action.data.photosProjectId
  };

这是扩展运算符 […]。扩展运算符可用于获取现有数组并向其中添加另一个元素，同时仍保留原始数组。

例子：

case actionTypes.PHOTOS_UPDATE:
  return [
    ...state,
    Object.assign({}, {
      photos:action.data.photos,
      photosTeamId:action.data.photosTeamId,
      photosProjectId:action.data.photosProjectId
    })
  ];