如何实现循环打印的唯一身份？

Question

我试图循环JSON格式，但是它没能运行起来。当我正确地循环"id_first" print 1 和 2 时，循环调用仍然没有定义ID。如何实现循环打印的唯一身份？

我的代码：

$(document).ready(function() {
   $.ajax({
     url: "http://192.168.1.190/tmp/data.json",
     method: "GET",
     success: function(data) {
       var id_first = [];

       for (var i in data) {
         id_first.push(data[i].id_first);
         alert(data[i].id_first);
       }
     },
     error: function(data) {
       console.log('error');
     }
   });
});

数据：

 [{
   "id_first": "1",
   "data_first": "1"
 }, {
   "id_first": "2",
   "data_first": "2"
 }, {
   "id_second": "1",
   "data_second": "1"
 }, {
   "id_second": "2",
   "data_second": "2"
 }]

Answer 1

Check whether id_first exist with data[i].id_first != undefined inside loop if yes then push into Array. So only valid(not undefined) will be added to id_first array

 var id_first=[]
var data =  [{
    "id_first": "1",
    "data_first": "1"   }, {
    "id_first": "2",
    "data_first": "2"  },  {
    "id_second": "1",
    "data_second": "1"  }, {
    "id_second": "2",
    "data_second": "2"  }]
     for(var i in data) {
     if(data[i].id_first != undefined){
          id_first.push(data[i].id_first);
          alert(data[i].id_first);
          }
     }
      console.log(id_first);

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