Node中Object.entries()返回异常结果的原因及解决咨询

问题场景 #

Node.js环境中，dbResultsArr是通过dbResultsArr = [...doc[result]]从Mongoose文档中解构得到的对象数组。循环中console.log(resultObj)能正常显示业务属性，但调用Object.entries(resultObj)时，返回的是包含__parentArray、_doc等Mongoose内部属性的数组，导致无法生成预期的myStr字符串。

相关代码 #

let ixi = 0;
for(const r of dbResultsArr){
  ixi++

  const resultObj = new Object(r);
  // without this console.log('Object.entries(r)', Object.entries(r)); was not working

  if(ixi === 1) {
    // see output below
    console.log('r', resultObj);  
    console.log('Object.entries(resultObj)', Object.entries(resultObj));              
  }

  let resultsV2Obj = {
    searchType: searchType,
  };

  let myStr = '';
  for (const [key, value] of Object.entries(resultObj)) {
    
    if(ixi === 1) {
     // see output below
      console.log('key of r - ', `${key}`);
    }

    if(key === 'pan') {
      resultsV2Obj.pan = value;
      
    } else if(key !== '_id' && key !== '__v') {
      myStr += `${key}: ${value}; `
    }
  }
  resultsV2Obj.nameDetails = myStr;
  newCheckObj.pmlaCheckResultsV2.push(resultsV2Obj);
}

控制台输出 #

r {
  _id: 610796d7cb5778deff3ef9bb,
  entity: 'Order in the matter of Infrastructures Limited and its Directors',
  name: 'Kumar Sharma',
  pan: 'xxxxx',
  orderDate: '02/11/2015\n\n\n03/10/2016',
  orderDetail: 'Restrained the entity from .....',
  __v: 0
}


Object.entries(resultObj) [
  [
    '__parentArray',
    [ [Object], [Object], [Object], [Object], [Object], [Object] ]
  ],
  [ '__index', 0 ],
  [ '$isDocumentArrayElement', true ],
  [
    '$__',
    InternalCache {
      strictMode: true,
      selected: undefined,
      shardval: undefined,
      saveError: undefined,
      validationError: undefined,
      adhocPaths: undefined,
      removing: undefined,
      inserting: undefined,
      saving: undefined,
      version: undefined,
      getters: {},
      _id: 610796d7cb5778deff3ef9bb,
      populate: undefined,
      populated: undefined,
      wasPopulated: false,
      scope: undefined,
      activePaths: [StateMachine],
      pathsToScopes: {},
      cachedRequired: {},
      session: null,
      '$setCalled': Set(0) {},
      ownerDocument: [Object],
      fullPath: 'sebiResultsFM',
      emitter: [EventEmitter],
      '$options': [Object]
    }
  ],
  [ 'isNew', false ],
  [ 'errors', undefined ],
  [ '$locals', {} ],
  [ '$op', null ],
  [
    '_doc',
    {
      _id: 610796d7cb5778deff3ef9bb,
      entity: 'Order in the matter of Infrastructures Limited and its Directors',
      name: 'Kumar Sharma',
      pan: 'xxxxx',
      orderDate: '02/11/2015\n\n\n03/10/2016',
      orderDetail: 'Restrained the entity from .....',
      __v: 0
    }
  ],
  [ '$init', true ]
]


key of r -  __parentArray
key of r -  __index
key of r -  $isDocumentArrayElement
key of r -  $__
key of r -  isNew
key of r -  errors
key of r -  $locals
key of r -  $op
key of r -  _doc
key of r -  $init

预期myStr结果 #

entity: 'Order in the matter of Infrastructures Limited and its Directors'; name: 'Kumar Sharma'; orderDate: '02/11/2015\n\n\n03/10/2016'; orderDetail: 'Restrained the entity from .....'

问题原因 #

你处理的不是普通JavaScript对象，而是Mongoose Document实例。Mongoose重写了Document的toString/console.log方法，打印时只会展示_doc里的业务数据，但实际对象本身包含大量Mongoose内部管理的属性（比如__parentArray、$__等）。用new Object(r)复制的方式并没有剥离这些Mongoose的包装层，所以Object.entries会遍历到所有内部属性。

解决方法 #

只需把Mongoose Document转换为纯JavaScript对象即可，有几种常用方式：

方法1：使用Mongoose内置的toObject()方法 #

这是最推荐的方式，专门用来将Document转为普通JS对象：

// 替换原来的const resultObj = new Object(r);
const resultObj = r.toObject();

方法2：使用toJSON()方法 #

效果和toObject()类似，部分场景下会自动应用schema里的transform规则：

const resultObj = r.toJSON();

方法3：直接提取_doc属性 #

Document的业务数据都存在_doc属性里，可以直接取用：

const resultObj = {...r._doc}; // 解构复制，避免直接修改原对象

方法4：JSON序列化再反序列化 #

通用的对象转换方式，适合任何场景，但性能略低：

const resultObj = JSON.parse(JSON.stringify(r));

修改后再运行，Object.entries(resultObj)就只会遍历你的业务属性，生成预期的myStr字符串。

内容的提问来源于stack exchange，提问作者hemant