json.stringify n'est pas une erreur de fonction en JavaScript

Je suis en utilisant la connexion, inscription Facebook de l'API JavaScript dans un plugin WordPress. J'ai eu cette erreur

json.stringify is not a function error at JavaScript.

Quel est le problème? J'utilise ce code:

<div id="fb-root"></div>
<script type="text/javascript">
var button;
var userInfo;
window.fbAsyncInit = function() {
FB.init({ appId: '154333274632806',
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>