如何从另一个对象向 json 对象中添加数据？

Question

我有一个包含一些数据的数据对象，现在我想创建另一个对象mapdata2，它与数据具有相同的结构。但是我的代码不起作用，并且还显示了一些语法错误。 我在其中创建了 mapdata2 对象和空特征数组。
它显示一个错误：

TypeError: i.features 未定义

<script>      
data = {"type": "FeatureCollection",
        "features": [
           {
                "type": "Feature", 
              "properties": 
              {
                "title": "ABC", "startDate": 1100, "endDate": 1200, "latitude": 60.814, "longitude": 11.845, "content": "content." 
              },
              "geometry": 
              {
                "type": "Point","coordinates": [ 60.814, 11.845, 1]
              } 
           },
           {
                "type": "Feature", 
              "properties": 
              {
                "title": "XYZ", "startDate": 1100, "endDate": 1200, "latitude": 40.814, "longitude": 15.845, "content": "content." 
              },
              "geometry": 
              {
                "type": "Point","coordinates": [ 40.814, 15.845, 1]
              } 
           },

         ]
     }
               mapdata2 = {
                  "type": "FeatureCollection",
                  "features" : []
                };

                for(i in data){
                    console.log(i);
                          mapdata2.features.push({
                            type:"Feature",
                            properties : { title: i.features.properties.title, startDate: i.features.properties.startDate, endDate: i.features.properties.endDate latitude: i.features.properties.latitude, longitude: i.features.properties.longitude, content: i.features.properties.content },
                            geometry : { type: "Point", coordinates: i.features.geometry.coordinates }
                        })
                  }
                  console.log(mapdata2);

 </script>

Answer 1

发生这种情况是因为您尝试访问 i 中的每个 i data，但第一个 i 是 "type" 并且它没有 features。

所以我修改了您的代码，以便您只对“功能”进行迭代，并且针对每个功能执行您所做的操作，现在它可以正常工作了。

data = {
  "type": "FeatureCollection",
  "features": [{
      "type": "Feature",
      "properties": {
        "title": "ABC",
        "startDate": 1100,
        "endDate": 1200,
        "latitude": 60.814,
        "longitude": 11.845,
        "content": "content."
      },
      "geometry": {
        "type": "Point",
        "coordinates": [60.814, 11.845, 1]
      }
    },
    {
      "type": "Feature",
      "properties": {
        "title": "XYZ",
        "startDate": 1100,
        "endDate": 1200,
        "latitude": 40.814,
        "longitude": 15.845,
        "content": "content."
      },
      "geometry": {
        "type": "Point",
        "coordinates": [40.814, 15.845, 1]
      }
    },

  ]
}
mapdata2 = {
  "type": "FeatureCollection",
  "features": []
};

data.features.forEach((feature) => {
  mapdata2.features.push({
    type: "Feature",
    properties: {
      title: feature.properties.title,
      startDate: feature.properties.startDate,
      endDate: feature.properties.endDate,
      id: feature.properties.id,
      latitude: feature.properties.latitude,
      longitude: feature.properties.longitude,
      content: feature.properties.content
    },
    geometry: {
      type: "Point",
      coordinates: feature.geometry.coordinates
    }
  })

});
console.log(mapdata2);

Answer 2

如果您只是想将 json 列表复制到 mapdata2，则根本不需要映射或循环。

mapdata2.features = data.features
console.log(mapdata2);

这将完成您希望完成的任务，而无需循环。

    
data = {"type": "FeatureCollection",
        "features": [
           {
                "type": "Feature", 
              "properties": 
              {
                "title": "ABC", "startDate": 1100, "endDate": 1200, "latitude": 60.814, "longitude": 11.845, "content": "content." 
              },
              "geometry": 
              {
                "type": "Point","coordinates": [ 60.814, 11.845, 1]
              } 
           },
           {
                "type": "Feature", 
              "properties": 
              {
                "title": "XYZ", "startDate": 1100, "endDate": 1200, "latitude": 40.814, "longitude": 15.845, "content": "content." 
              },
              "geometry": 
              {
                "type": "Point","coordinates": [ 40.814, 15.845, 1]
              } 
           },

         ]
     }
mapdata2 = {
  "type": "FeatureCollection",
  "features" : []
};

mapdata2.features = data.features
console.log(mapdata2);

Answer 3

您似乎想复制该对象。您可以简单地执行以下操作。

var mapdata2 = JSON.parse(JSON.stringify(data));

顺便说一句，您收到错误“TypeError: i.features is undefined”，因为 i 是表示对象键的字符串。它将采用值“类型”和“特征”。

要遍历数组 data.features 中的项目，您应该这样做：

for (var i=0;i<data.features.length;i++) {
  var item = data.features[i];
}

Answer 4

这里有一些错误：

• in for bucle 中的关键字迭代的是键，而不是值，我知道这是你想要复制数据的方式。
• 您正在尝试访问数组 features 的属性 properties，而不先访问该数组的索引。

将代码的最后一部分更改为：

for(const feature of data.features){
    mapdata2.features.push({
        type:"Feature",
        properties : { title: feature.properties.title, startDate: feature.properties.startDate, endDate: feature.properties.endDate, latitude: feature.properties.latitude, longitude: feature.properties.longitude, content: feature.properties.content },
        geometry : { type: "Point", coordinates: feature.geometry.coordinates }
    })
}
console.log(mapdata2);

应该做的工作:)

但是，如果您只是想复制数据，我建议：

mapdata2 = {...data}
console.log(mapdata2)

Answer 5

保持您的风格的“快速修复”：

for(i of data.features) {
  console.log(i)
    mapdata2.features.push({
        type:"Feature",
        properties : { 
            title: i.properties.title, 
            startDate: i.properties.startDate, 
            endDate: i.properties.endDate, 
            id: i.properties.id, 
            latitude: i.properties.latitude, 
            longitude: i.properties.longitude, 
            content: i.properties.content },
        geometry : { 
            type: "Point",  
            coordinates: i.geometry.coordinates 
        }
    })
}