格式复杂嵌套 objects

Question

我之前在 gis 论坛（下面的 Alt）发过帖子，虽然 activity 很少，所以我在这里试试运气。从根本上说，我认为这也是一个 js object 数组问题。有很多类似的问题，但我无法找到适用于我必须处理的 object 结构的解决方案。

抛开注意事项；

问题： 从嵌套在 object 数组中的（未知）数量的 object 中获取返回的信息，经过解析以便提取它们，以人类可读的方式格式化和显示。例如;

Layer id  <--- currently returned as val.layer.id (see snippet)
key1 : value1 <
key2 : value2 <-- returns in console.log as Object at val.properties
key3 : value3 <

Layer id
key1 : value1
key2 : value2

Layer id...

我只需要每个 'features.layer.id' 及其关联的 'features.properties'，它们的键和值是未知的并且在层之间不同（object 位于 features.properties） .这些特征位置在MapBox中是一致的，所以这里的解决方案应该适用于未来的用户。

当前代码; 注释掉的是我尝试访问和显示所需值的分散。 'features' elementID 是信息面板。 features 否则返回嵌套 object（参见示例）。

concattedjson 当前在第一层标题的第一个字母上产生错误 ("unexpected token N")。

map.on('click', function (e) {
    map.featuresAt(e.point, {radius: 5, layer: lyrlist}, function (err, features) {
        if (err) throw err;

        var keys = Object.keys(features);
        var val = "";

        for (var i = 0; i < keys.length; i++) {
            val = features[keys[i]];
            //document.getElementById('features').innerHTML = '<b>'+val.layer.id+'</b>';
            //console.log(val.layer.id,val.properties);
            //console.log(val.properties); shows each layer properties on click
            //console.log(val.layer.id); shows each layer title on click
            //console.log(val);
            var lyrid = val.layer.id;
            var prop = val.properties;
            concattedjson = JSON.stringify(JSON.parse(lyrid).concat(JSON.parse(prop)));
        }   
    document.getElementById('features').innerHTML = concattedjson   
    //document.getElementById('features').innerHTML = JSON.stringify(val.layer, ['id'], 2);     
    //document.getElementById('features').innerHTML = JSON.stringify(val.properties, null, 2);          
    });
});

JSON 的样本包含两个 'layers'

    [
  {
    "layer": {
      "id": "Nature Improvement Area",
      "minzoom": 7,
      "interactive": true,
      "paint": {
        "fill-opacity": 0.3,
        "fill-color": "hsl(0, 24%, 24%)"
      },
      "type": "fill",
      "source": "mapbox://mbbdev.8uf2j3ka",
      "source-layer": "lcr_nia_v1_region",
      "layout": {
        "visibility": "visible"
      }
    },
    "type": "Feature",
    "geometry": null,
    "properties": {
      "NIA_Focu00": "Netherley Brook and Ditton Brook Corridor",
      "NIA_Focu01": "INSERT LINK TO PROFILE DOC",
      "NIA_Focus_": "07"
    },
    "id": 16
  },
  {
    "layer": {
      "id": "Liverpool City Region",
      "minzoom": 6,
      "interactive": true,
      "paint": {
        "fill-opacity": 0.2,
        "fill-antialias": true,
        "fill-color": "hsl(0, 4%, 40%)"
      },
      "type": "fill",
      "source": "mapbox://mbbdev.67id5f6x",
      "source-layer": "lcr_district_boundary_region",
      "filter": [
        "==",
        "$type",
        "Polygon"
      ]
    },
    "type": "Feature",
    "geometry": null,
    "properties": {
      "AREA_HA": 8618.7,
      "NAME": "Knowsley"
    },
    "id": 1
  }
]

站点：http://www.activenaturalist.org.uk/lcren/imap/mb.html（显示单击特征元素中的特征结构 object。
相似： Having trouble with mapbox GL layers; Access / process (nested) objects, arrays or JSON
替代： https://gis.stackexchange.com/questions/181005/extract-geojson-properties-dynamically-with-mapbox-gl

Answer 1

以下是如何迭代 features 对象，并从中创建人类可读的内容。评论中的解释：

map.on('click', function (e) {
    map.featuresAt(e.point, {
        radius: 5,
    }, function (err, features) {
        if (err) throw err;

        // Grab the 'ul' element with ID 'features' from the DOM            
        var featureList = document.getElementById('features');

        // Empty the list on every click
        featureList.innerHTML = '';

        // Iterate the features array
        for (var i = 0; i < features.length; i++) {

            // Create a listitem for each feature
            var featureItem = document.createElement('li');

            // Set the feature's listitem's content to the layer's ID
            featureItem.textContent = features[i].layer.id;

            // Append the featureitem to the featurelist
            featureList.appendChild(featureItem);

            // Create a new list for the item's properties
            var propertyList = document.createElement('ul');

            // Append the list to the feature's listitem
            featureItem.appendChild(propertyList);

            // Create convenience var for the properties object
            var properties = features[i].properties;

            // Iterate the properties object
            for (var property in properties) {

                // Create new listitem for every property
                var propertyItem = document.createElement('li');

                // Set property's listitem's textcontent to key/value
                propertyItem.textContent = property + ': ' + properties[property];

                // Append property's listitem to the feature's propertylist.
                propertyList.appendChild(propertyItem);

            }

        }

    });
});

这是一个关于 Plunker 的工作示例：http://plnkr.co/edit/iqntvRFTcWK1hgpzPBvX?p=preview

如果您想掌握对象属性的概念以及如何访问它们，您可能需要阅读此内容：

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Operators/Property_accessors

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