实现json集的一个参数

如何解决实现json集的一个参数

我有 JavaScript 语言的代码，当我输入 console.log(event) 时，输出是：

{"type":"FeatureCollection","features":[{"type":"Feature","id":"","geometry":null,"properties":{"GRAY_INDEX":176}}],"totalFeatures":"unkNown","numberReturned":1,"timeStamp":"2021-03-03T14:04:13.362Z","crs":null}

我想要“属性”部分中的“GRAY_INDEX”值。我应该怎么办？ 这是我的代码：

map.on('singleclick',function(evt) {
    document.getElementById('info').innerHTML = '';
    var view = map.getView();
    var viewResolution = view.getResolution();
    var url = UnTiled.getSource().getfeatureinfoUrl(
        evt['coordinate'],viewResolution,'epsg:3857',{'INFO_FORMAT': 'application/json'}
      );
      console.log(url);
      if (url) {
        fetch(url)
          .then(function (response) { return response.text(); })
          .then(function (html) {
            html;
            console.log(html);
          });
      }
      
     });

我试过了：

console.log(html["properties"]

但控制台说未定义

解决方法

如果您格式化了 json，您将能够更清楚地看到如何访问它：

{
  "type": "FeatureCollection","features": [
    {
      "type": "Feature","id": "","geometry": null,"properties": {
        "GRAY_INDEX": 176
      }
    }
  ],"totalFeatures": "unknown","numberReturned": 1,"timeStamp": "2021-03-03T14:04:13.362Z","crs": null
}

如果将上述内容分配给 html，那么要访问 GRAY_INDEX 值，您应该这样做：

html.features[0].properties.GRAY_INDEX

您希望首先使用 response.json() 而不是 response.text() 或在尝试访问之前添加 html = JSON.parse(html) 将响应解析为 JSON。

,

您似乎在参数“html”中获得了 JavaScript 对象的 JSON 表示，如果是这种情况，您首先需要将 JSON 解析为对象。比您想要访问功能的属性。 Features 是一个数组，所以如果你想获取所有元素的属性，你应该这样做：

var html = '{"type":"FeatureCollection","features":[{"type":"Feature","id":"","geometry":null,"properties":{"GRAY_INDEX":176}}],"totalFeatures":"unknown","numberReturned":1,"timeStamp":"2021-03-03T14:04:13.362Z","crs":null}';
var o = JSON.parse(html);
o.features.forEach(function(each,index) { 
  console.log(`index = ${index}\n`,each.properties);
});