在此示例上访问JSON数据时出现问题

Question

this is a json i have, is valid, but for some reason if I access this query.pages.length is "undefined"... how do i know the numebr of children of pages then? are they children?

  {
       "query-continue":{
          "allpages":{
             "gapfrom":"Tron (film)"
          }
       },
       "query":{
          "pages":{
             "174059":{
                "pageid":174059,
                "ns":0,
                "title":"Tron"
             },
             "29799461":{
                "pageid":29799461,
                "ns":0,
                "title":"Tron: Betrayal"
             },
             "2424602":{
                "pageid":2424602,
                "ns":0,
                "title":"Tron: Deadly Discs"
             },
             "25415189":{
                "pageid":25415189,
                "ns":0,
                "title":"Tron: Evolution"
             },
             "29958517":{
                "pageid":29958517,
                "ns":0,
                "title":"Tron: Evolution - Battle Grids"
             },
             "22547607":{
                "pageid":22547607,
                "ns":0,
                "title":"Tron: Legacy"
             },
             "29541046":{
                "pageid":29541046,
                "ns":0,
                "title":"Tron: Legacy (soundtrack)"
             },
             "11825742":{
                "pageid":11825742,
                "ns":0,
                "title":"Tron: Solar Sailer"
             },
             "8005401":{
                "pageid":8005401,
                "ns":0,
                "title":"Tron: The Ghost in the Machine"
             },
             "29487895":{
                "pageid":29487895,
                "ns":0,
                "title":"Tron: Uprising"
             }
          }
       }
    }

Answer 1

I wrote this code to count length of pages :

count = 0;
for (var key in netData.query.pages) {
count = count + 1;
}
alert(count);

Answer 2

query.pages is an object, not an array. If you are in control of generating the json, you can make it an array of objects instead:

"query":{
  "pages":[
    {
      "pageid":174059,
      "ns":0,
      "title":"Tron"
    },
    {
      "pageid":29799461,
      "ns":0,
      "title":"Tron: Betrayal"
    },
    {
      "pageid":2424602,
      "ns":0,
      "title":"Tron: Deadly Discs"
    }
  ]
}

then you can use query.pages.length. using an array is fine, since the key is just the pageid.

Answer 3

I had to deal with this... you'll need to iterate through each page in pages, and check for hasOwnProperty, or if all are numbered...

var count = 0;
for (var key in query.pages) {
  //local page variable
  var page = query.pages[key];

  //page isn't what you're looking for
  if (!page || page.pageid != key) continue;

  //increase count
  count++;

  //do something with page
}

I've seen this kind of sloppy json before, and the engineer should be shot.