javascript - 复杂的 JSON obj 和 jQuery 或 Javascript 映射到特定的键、值

Question

我正在绞尽脑汁想弄明白这个问题。它不应该这么难。我显然错过了一步。

我正在从 openaq.org 中提取数据

我取回的对象是基于 JSON 对象的。
现在，我正在使用 jQuery 来解析对象，我正在获取包含我想要的特定参数的对象的子部分，但我无法获取特定的键值对。

对象不会一直以相同的顺序返回。所以当我最初尝试建立我的电话时，我做了类似的事情 obj.results.measurements[0]。

因为 obj 可以以随机顺序返回，所以我再次返回查找键值对，但它是错误的值，让我无法看清。

也就是说，我看过use jQuery's find() on JSON object并且出于某种原因无法从 openaq.org 提供的对象中获得我需要的东西。

对象的一个​​版本如下所示:

{"meta":{"name":"openaq-api","license":"CC BY 4.0d","website":"https://u50g7n0cbj.execute-api.us-east-1.amazonaws.com/","page":1,"limit":100,"found":1},"results":[{"location":"Metro Lofts","city":null,"country":"US","coordinates":{"latitude":39.731,"longitude":-104.9888},"measurements":[{"parameter":"pm10","value":49.9,"lastUpdated":"2021-08-09T20:49:38+00:00","unit":"µg/m³"},{"parameter":"pm1","value":24,"lastUpdated":"2021-08-09T20:49:38+00:00","unit":"µg/m³"},{"parameter":"um100","value":0,"lastUpdated":"2021-08-09T20:49:38+00:00","unit":"particles/cm³"},{"parameter":"um025","value":0.28,"lastUpdated":"2021-08-09T20:49:38+00:00","unit":"particles/cm³"},{"parameter":"um010","value":4.1,"lastUpdated":"2021-08-09T20:49:38+00:00","unit":"particles/cm³"},{"parameter":"pm25","value":41.1,"lastUpdated":"2021-08-09T20:49:38+00:00","unit":"µg/m³"}]}]}

我正在尝试获取“pm25”值。

我试过的代码是这样的:

function getAirQualityJson(){
    $.ajax({
      url: 'https://api.openaq.org/v2/latest?coordinates=39.73915,-104.9847',
      type: 'GET',
      dataType: "json"
     // data: data ,
  }).done(function(json){
 console.log("the json is" + JSON.stringify(json));
 console.log("the json internal is" + JSON.stringify(json.results));
 var obj = json.results;
 var pm25 = "";
 //console.log(JSON.stringify(json.results.measurements[0]["parameter"]));
 $.each(json.results[0], function(i,items){
   //console.log("obj item:" + JSON.stringify(obj[0].measurements));
    $.each(obj[0].measurements, function(y,things){
    //console.log("each measurement:" + JSON.stringify(obj[0].measurements[0].value));//get each measurement
    //pm 2.5
    //Can come back in random order, get value from the key "pm25" 
    // pm25 = JSON.stringify(obj[0].measurements[2].value);
    pm25 = JSON.stringify(obj[0].measurements[0].value); 

console.log("pm25 is: " + pm25); // not right
  });
});

//Trying Grep and map below too.  Not working
jQuery.map(obj, function(objThing) 
{ console.log("map it 1:" + JSON.stringify(objThing.measurements.parameter));
  if(objThing.measurements.parameter === "pm25"){
     //  return objThing; // or return obj.name, whatever.
       console.log("map it:" + objThing);
  }else{

    console.log("in else for pm25 map");
  }
});


jQuery.grep(obj, function(otherObj) {
  //return otherObj.parameter === "pm25";
  console.log("Grep it" + otherObj.measurements.parameter === "pm25");
});


});
}
getAirQualityJson();

https://jsfiddle.net/7quL0asz/

如您所见，循环通过 I 运行我尝试了 [2]，这是 'pm25' 值的原始位置，但随后它切换到第 3 或第 4 个位置，因此它是不可预测的。

我尝试了 jQuery Grep 和 Map，但返回未定义或错误。

所以我的问题是，我将如何解析它以获取“pm25”键值。之后，如果我需要的话，我可以得到其余的。

预先感谢您提供的所有帮助。

Answer 1

您可以使用 array#find和 optional chaining为此，

因为我们正在使用可选链，所以如果缺少属性，将返回undefined。

演示:

let data = {"meta":{"name":"openaq-api","license":"CC BY 4.0d","website":"https://u50g7n0cbj.execute-api.us-east-1.amazonaws.com/","page":1,"limit":100,"found":1},"results":[{"location":"Metro Lofts","city":null,"country":"US","coordinates":{"latitude":39.731,"longitude":-104.9888},"measurements":[{"parameter":"pm10","value":49.9,"lastUpdated":"2021-08-09T20:49:38+00:00","unit":"µg/m³"},{"parameter":"pm1","value":24,"lastUpdated":"2021-08-09T20:49:38+00:00","unit":"µg/m³"},{"parameter":"um100","value":0,"lastUpdated":"2021-08-09T20:49:38+00:00","unit":"particles/cm³"},{"parameter":"um025","value":0.28,"lastUpdated":"2021-08-09T20:49:38+00:00","unit":"particles/cm³"},{"parameter":"um010","value":4.1,"lastUpdated":"2021-08-09T20:49:38+00:00","unit":"particles/cm³"},{"parameter":"pm25","value":41.1,"lastUpdated":"2021-08-09T20:49:38+00:00","unit":"µg/m³"}]}]}

let found = data?.results?.[0]?.measurements?.find?.(
    ({ parameter }) => parameter === "pm25"
);

console.log(found);