jQuery ajax json response has length undefined and incorrect data

I'm trying to grab a dictionary object which is converted to json object in server side, (along with correct content-type header), but for some reason, even though I can access part of the data, other parts don't show up and json object in jquery has length equal to 0.

Here is my jquery call:

$.ajax({
        type : "POST",
        url : cl._url,
        //data : 'text='+text,  
  data: "{}",
  contentType: "application/json; charset=utf-8",
        dataType : "json",
        error : function(XHR, status, error) {
            alert("There was an error processing the request.\n\n"+XHR.responseText);
        },
        success : function(json){
            if (!json.length) {
                alert('There are no incorrectly spelled words...'+json[0]+ '  ' + json.length);
            } else {
                // highlight bad words
            }
         开发者_如何学C   cl.$container.html(html);   
            // execute callback function, if any
            (callback != undefined) && callback(); 
        }
    });

I usually get the alert box with this code, and json[0] prints out 99 as expected. But json.length is "undefined". So in a sense, the json returned is right but my code will not detect it and use it.

When I go directly to my ashx page where my json data is printed on the screen, I get this json object:

{"id":1,"json":[5,10,15,20],"0":"99"}

Just a sample json output. So how come json.length is not 3???

UPDATE: So I changed my asp.net code, from Dictionary to List, and then added the same values. And suddenly, length is functioning now. ?!?!?! So objects don't have lengths in javascript?

---

Objects don't have a length property unless you give them one. Arrays do, but arrays are created with [] not {}.

If you want to know how many properties an object has, you have to loop over them and count them:

var count = 0;
for (var foo in bar) {
    if (bar.hasOwnProperty(foo) {
        count++;
    }
}

---

Best way to debug this is to inspect the response under Firebug console. See if you are even getting back a valid response.

http://getfirebug.com/

---

You can convert your object to JSON using :

var jsonVariable= JSON.stringify(objectVariable);
var jsonVariableLength = jsonVariable.length ;

And print the length :

alert('Length : ' + jsonVariableLength );