json.stringify is not a function error at JavaScript

I'm using login, registration Facebook API with JavaScript in a WordPress plugin. I got this error

json.stringify is not a function error at JavaScript.

What is the issue? I use this code:

<div id="fb-root"></div>
<script type="text/javascript">
    var button;
    var userInfo;

    window.fbAsyncInit = function() {
        FB.init({ appId: '15开发者_运维问答4333274632806',
            status: true,
            cookie: true,
            xfbml: true,
            oauth: true});

        showLoader(true);

        function updateButton(response) {
            button       =   document.getElementById('fb-auth');
            userInfo     =   document.getElementById('user-info');

            if (response.authResponse) {
                //user is already logged in and connected
                FB.api('/me', function(info) {
                    login(response, info);
                });

                button.onclick = function() {
                    FB.logout(function(response) {
                        logout(response);
                    });
                };
            }
            else {
                //user is not connected to your app or logged out
                button.innerHTML = 'Login';
                button.onclick = function() {
                    showLoader(true);
                    FB.login(function(response) {
                        if (response.authResponse) {
                            FB.api('/me', function(info) {
                                login(response, info);
                            });
                        } else {
                            //user cancelled login or did not grant authorization
                            showLoader(false);
                        }
                    }, {scope:'email,user_birthday,status_update,publish_stream,user_about_me'});
                }
            }
        }

        // Run once with current status and whenever the status changes.
        FB.getLoginStatus(updateButton);
        FB.Event.subscribe('auth.statusChange', updateButton);
    };
    (function() {
        var e = document.createElement('script'); e.async = true;
        e.src = document.location.protocol
            + '//connect.facebook.net/en_US/all.js';
        document.getElementById('fb-root').appendChild(e);
    }());

    function login(response, info){
        if (response.authResponse) {
            var accessToken                                =   response.authResponse.accessToken;

            userInfo.innerHTML                             = '<img src="https://graph.facebook.com/' + info.id + '/picture">' + info.name
                                                             + "<br /> Your Access Token: " + accessToken;
            button.innerHTML                               = 'Logout';
            showLoader(false);
            document.getElementById('other').style.display = "block";
        }
    }

    function logout(response){
        userInfo.innerHTML                             =   "";
        document.getElementById('debug').innerHTML     =   "";
        document.getElementById('other').style.display =   "none";
        showLoader(false);
    }

    //stream publish method
    function streamPublish(name, description, hrefTitle, hrefLink, userPrompt){
        showLoader(true);
        FB.ui(
        {
            method: 'stream.publish',
            message: '',
            attachment: {
                name: name,
                caption: '',
                description: (description),
                href: hrefLink
            },
            action_links: [
                { text: hrefTitle, href: hrefLink }
            ],
            user_prompt_message: userPrompt
        },
        function(response) {
            showLoader(false);
        });
    }

    function showStream(){
        FB.api('/me', function(response) {
            //console.log(response.id);
            streamPublish(response.name, 'I like the articles of Thinkdiff.net', 'hrefTitle', 'http://thinkdiff.net', "Share thinkdiff.net");
        });
    }

    function share(){
        showLoader(true);
        var share = {
            method: 'stream.share',
            u: 'http://thinkdiff.net/'
        };

        FB.ui(share, function(response) {
            showLoader(false);
            console.log(response);
        });
    }

    function graphStreamPublish(){
        showLoader(true);

        FB.api('/me/feed', 'post',
            {
                message     : "I love thinkdiff.net for facebook app development tutorials",
                link        : 'http://ithinkdiff.net',
                picture     : 'http://thinkdiff.net/iphone/lucky7_ios.jpg',
                name        : 'iOS Apps & Games',
                description : 'Checkout iOS apps and games from iThinkdiff.net. I found some of them are just awesome!'
        },
        function(response) {
            showLoader(false);

            if (!response || response.error) {
                alert('Error occured');
            } else {
                alert('Post ID: ' + response.id);
            }
        });
    }

    function fqlQuery(){
        showLoader(true);

        FB.api('/me', function(response) {
            showLoader(false);

            //http://developers.facebook.com/docs/reference/fql/user/
            var query       =  FB.Data.query('select name, profile_url, sex, pic_small from user where uid={0}', response.id);
            query.wait(function(rows) {
               document.getElementById('debug').innerHTML =
                 'FQL Information: '+  "<br />" +
                 'Your name: '      +  rows[0].name                                                            + "<br />" +
                 'Your Sex: '       +  (rows[0].sex!= undefined ? rows[0].sex : "")                            + "<br />" +
                 'Your Profile: '   +  "<a href='" + rows[0].profile_url + "'>" + rows[0].profile_url + "</a>" + "<br />" +
                 '<img src="'       +  rows[0].pic_small + '" alt="" />' + "<br />";
             });
        });
    }

    function setStatus(){
        showLoader(true);

        status1 = document.getElementById('status').value;
        FB.api(
          {
            method: 'status.set',
            status: status1
          },
          function(response) {
            if (response == 0){
                alert('Your facebook status not updated. Give Status Update Permission.');
            }
            else{
                alert('Your facebook status updated');
            }
            showLoader(false);
          }
        );
    }

    function showLoader(status){
        if (status)
            document.getElementById('loader').style.display = 'block';
        else
            document.getElementById('loader').style.display = 'none';
    }

</script>

<h3>New JavaScript SDK & OAuth 2.0 based FBConnect Tutorial | Thinkdiff.net</h3>
<button id="fb-auth">Login</button>
<div id="loader" style="display:none">
    <img src="ajax-loader.gif" alt="loading" />
</div>

<br />
<div id="user-info"></div>
<br />
<div id="debug"></div>

<div id="other" style="display:none">
    <a href="#" onClick="showStream(); return false;">Publish Wall Post</a> |
    <a href="#" onClick="share(); return false;">Share With Your Friends</a> |
    <a href="#" onClick="graphStreamPublish(); return false;">Publish Stream Using Graph API</a> |
    <a href="#" onClick="fqlQuery(); return false;">FQL Query Example</a>

    <br />
    <textarea id="status" cols="50" rows="5">Write your status here and click 'Status Set Using Legacy Api Call'</textarea>
    <br />
    <a href="#" onClick="setStatus(); return false;">Status Set Using Legacy Api Call</a>
</div>

You can find a link to the code for json.stringify here -

http://www.json.org/js.html

If you add that to your code then the error should go away.

Alternatively, you could add a reference to this script to your code -

<script src="http://ajax.cdnjs.com/ajax/libs/json2/20110223/json2.js"></script>

What browser are you using? Not every browser supports native JSON parsing like you are trying. Also, it should be:

JSON.stringify