Javascript对象-整体对象中缺少的功能，但仍然存在

Javascript objects - feature missing from overall object, yet exists

本文关键字：对象 功能 存在 Javascript      更新时间：2023-09-26

这里有个奇怪的问题。我正在运行Node/Express/Mongoose/Leaflet。我从数据库中提取一个位置数组，一旦回调启动，我就会迭代这些位置，找到一堆处理每个位置的字符串段落。然后，我尝试将段落数组附加到每个位置对象，然后将位置数组附加到GeoJSON FeatureCollection。

Location.find({}, { _id: 0 }, function (err, locations) {
    if (err) {
        console.log('DB Error loading all locations');
    res.redirect('/');
} else {
    var num = 0;
    console.log("Beginning finding all passages");
    locations.forEach(function (location) {
    num++;
    console.log("Looking up a location");
    Passage.find({"placekey": location.properties.placekey}, function (err, passages) {
        if (err) {
            console.log('DB Error finding passage for: ' + location.properties.placekey);
        } else {
            console.log("Passage was found!");
            location.properties.passages = passages[0]; //take first passage
            num--;
        }
        if (num === 0) {
            console.log("All passages were found!");
            var featureCollection = {
                "type": "FeatureCollection",
                "features": locations
            };
            console.log(featureCollection);
            console.log(featureCollection.features[0].properties);
            console.log(featureCollection.features[0].properties.passages);
            res.json(featureCollection);
            console.log("JSON sent over!");
        }
    });
});

记录featureCollection让我的featureCollection没有任何段落：

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "num_books": 62,
        "Age": "Built 1078",
        "ID": "",
        "num_mentions": 325,
        "Place": "The Tower",
        "placekey": "TheTower",
        "GeocodeNotes": "",
        "Notes": "Built on the site of Roman fortifications, the central part of the Tower, known as the White Tower, was built in 1078 by William the Conqueror. Subsequent rings of fortification were added later. It was used as a royal residence as well as a prison and place of execution until Elizabethan times. England's child king, Edward V, and his brother were murdered in the Tower in 1483 supposedly by their uncle, Richard III.",
        "Class": "n/a",
        "Type": "Landmark"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [
          -0.076111,
          51.508056
        ]
      }
    },
   // more objects

无段落属性。

然而，当我使用console.log（featureCollection.features[0].properties.passions）时，我得到了第一段：

 {
  "_id": "51deebdbb2b5de1b8b6d7da1",
  "index": 27100,
  "bookid": 1,
  "author": "Ainsworth, William",
  "place": "The Tower",
  "placekey": "TheTower",
  "query_ok": true,
  "year": 1839,
  "corpus": "Chadwyck",
  "fn": "/Volumes/LilaData1/Plain2/Chadwyck/lilaBookId_00149.txt",
  "context_a": "The course of the carpenter's meditations was here...
  //more features
}

此外，使用（如果featureCollection.features[0].properties中的"passages"）会使我为true。事实上，我可以设置从服务器向其发送JSON响应的条件，并且我的featureCollection（没有段落）将被发送。。。

很抱歉发了这么长的帖子，但我真的快疯了。有什么想法吗？

谢谢！：）

问题是在Document上定义的检查干扰了console.log操作。此检查不考虑添加到文档实例的属性（如documentinst.prp=1）。

要解决您的问题，请尝试在返回文档上使用toJSON，然后将属性附加到返回对象

在您的情况下，

var _locations = [];
locations.forEach(function(_location){ // actual mongoose document
  var location;
  location = _location.toJSON(); // do toJSON on the _location mongoose document
  _locations.push(location); //push this object into the new array _locations
  ....logic for passages...
  //imp - add properties to the location object return from toJSON
  if (num === 0) {
    ...
     var featureCollection = {
            "type": "FeatureCollection",
            "features": _locations // use the new _locations array
      };
    ...
 }

})；

当res.json（obj）被调用时，这个方法要做的第一件事就是调用json.stringfy（obj；

如果obj定义了toJSON，那么从调用obj.toJSON（）返回的对象将由JSON.stringify.使用

如果您在一个对象上提供一个toJSON方法，并且它被编码为返回另一个对象而不是定义toJSON的对象，JSON.stringify将对这个新对象进行操作。您将能够查看这个新对象的属性，而不是实际对象的属性。

res.json依赖于toJSON。

console.log依赖inspect。

我刚刚用这个代码片段演示了上面的内容，

var util = require('util');
function Document(){this._doc = {};}
Document.prototype.inspect = function(){return util.inspect(this._doc)};
Document.prototype.toJSON = function(){return this.inspect()};
var docInst = new Document();
docInst.newProp = 'abc'; //property never shows up in console.log / JSON.stringify
docInst._doc._newProp = "_abc";
console.log(docInst);
JSON.stringify(docInst);
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