parsing JSON using Jquery

Question

I've got a page that will get a quick login check and access a web service for some JSON data. The data it's returning looks like this:

{ 'RESPONSE' : 'INVALID','CAMPAIGNID' : '0','MORELINK' : '' } 

The code I'm using to get this data and attempt to pop a modal window based on the information is:

   $.ajax({
            type: "POST",
            contentType: "application/json; charset=utf-8",
            url: "Login.asmx/Logon",
            data: strData,
            dataType: "json",
            success: function (response) {
                $('#divResp').html(response.d);
                $(response.d).each(function(index,item){
                    alert(item.campaignid);
                });
                if (res.indexOf('invalid') >= 0){                       
                    //invalid account information UNP                       
                    foo = "You entered an invalid account number or password";
                    showDialog('screenActivate.asp',test_imgName);
                } 
                if (res.indexOf('none') >=0) {
                    //do not deliver splash screen
                    foo = "No splash screen for YOU!";
                } 
                if (res.indexOf('error') >=0) {
                    //general error
                    foo = "You entered an error";
                }
                if (res.indexOf('frozen') >=0) {
                    //member is locked out from numberous failed attempts
                    foo = "You have too many failed attempts.  Your account has been locked";
                }
                if (res.indexOf('.png') >=0) {
                    imgName = (response.d);
                    showDialog('screenActivate.asp',test_imgName);
                }
                alert(foo);
                $('#divResp').html(response.d);
            }
        });
        $('#divQuery').ajaxError(function(evt, request, settings){
            $('#divResp').html("Web services timeout.  Please try again.");             
        });
    }

The challenge is, either I get no information (Undefined) or as is with this current iteration, an error from Firebug that states uncaught exception: Syntax error, unrecognized expression: 'INVALID'

Am I not parsing the JSON response properly?

Relevant comment to answer

I pasted: "d":"{ 'RESPONSE' : 'INVALID','CAMPAIGNID' : '0','MORELINK' : '' } " into the jsonlint.com and that tool says the JSON is valid. When I attempt to loop through response.d with an each statement, it seems to go character by character.

Answer 1

JSON spec requires the use of double quotes (") instead of single quotes (')

Official JSON string parsing Diagram (from http://www.json.org)

http://www.json.org/string.gif

in response to your comment...

ok, here's the deal...

"d":"{ 'RESPONSE' : 'INVALID','CAMPAIGNID' : '0','MORELINK' : '' } "

IS valid JSON... but it is simply an object with a d property that contains the string...

"{ 'RESPONSE' : 'INVALID','CAMPAIGNID' : '0','MORELINK' : '' } "

data that would work the way you expect would look like this...

{"d": {"RESPONSE":"INVALID","CAMPAIGNID":"0","MORELINK":""}}

Answer 2

In addition to @jondavidjohn's answer (+1), you're also referencing the variable res, which is not defined.