Develop Reference

.fail() fails to execute when ajax request is not successful [duplicate]

Is it possible to catch an error when using JSONP with jQuery? I've tried both the $.getJSON and $.ajax methods but neither will catch the 404 error I'm testing. Here is what I've tried (keep in mind that these all work successfully, but I want to handle the case when it fails):
jQuery.ajax({
type: "GET",
url: handlerURL,
dataType: "jsonp",
success: function(results){
alert("Success!");
},
error: function(XMLHttpRequest, textStatus, errorThrown){
alert("Error");
}
});
And also:
jQuery.getJSON(handlerURL + "&callback=?",
function(jsonResult){
alert("Success!");
});
I've also tried adding the $.ajaxError but that didn't work either:
jQuery(document).ajaxError(function(event, request, settings){
alert("Error");
});

Here's my extensive answer to a similar question.
Here's the code:
jQuery.getJSON(handlerURL + "&callback=?",
function(jsonResult){
alert("Success!");
})
.done(function() { alert('getJSON request succeeded!'); })
.fail(function(jqXHR, textStatus, errorThrown) { alert('getJSON request failed! ' + textStatus); })
.always(function() { alert('getJSON request ended!'); });

It seems that JSONP requests that don't return a successful result never trigger any event, success or failure, and for better or worse that's apparently by design.
After searching their bug tracker, there's a patch which may be a possible solution using a timeout callback. See bug report #3442. If you can't capture the error, you can at least timeout after waiting a reasonable amount of time for success.

Detecting JSONP problems
If you don't want to download a dependency, you can detect the error state yourself. It's easy.
You will only be able to detect JSONP errors by using some sort of timeout. If there's no valid response in a certain time, then assume an error. The error could be basically anything, though.
Here's a simple way to go about checking for errors. Just use a success flag:
var success = false;
$.getJSON(url, function(json) {
success = true;
// ... whatever else your callback needs to do ...
});
// Set a 5-second (or however long you want) timeout to check for errors
setTimeout(function() {
if (!success)
{
// Handle error accordingly
alert("Houston, we have a problem.");
}
}, 5000);
As thedawnrider mentioned in comments, you could also use clearTimeout instead:
var errorTimeout = setTimeout(function() {
if (!success)
{
// Handle error accordingly
alert("Houston, we have a problem.");
}
}, 5000);
$.getJSON(url, function(json) {
clearTimeout(errorTimeout);
// ... whatever else your callback needs to do ...
});
Why? Read on...
Here's how JSONP works in a nutshell:
JSONP doesn't use XMLHttpRequest like regular AJAX requests. Instead, it injects a <script> tag into the page, where the "src" attribute is the URL of the request. The content of the response is wrapped in a Javascript function which is then executed when downloaded.
For example.
JSONP request: https://api.site.com/endpoint?this=that&callback=myFunc
Javascript will inject this script tag into the DOM:
<script src="https://api.site.com/endpoint?this=that&callback=myFunc"></script>
What happens when a <script> tag is added to the DOM? Obviously, it gets executed.
So suppose the response to this query yielded a JSON result like:
{"answer":42}
To the browser, that's the same thing as a script's source, so it gets executed. But what happens when you execute this:
<script>{"answer":42}</script>
Well, nothing. It's just an object. It doesn't get stored, saved, and nothing happens.
This is why JSONP requests wrap their results in a function. The server, which must support JSONP serialization, sees the callback parameter you specified, and returns this instead:
myFunc({"answer":42})
Then this gets executed instead:
<script>myFunc({"answer":42})</script>
... which is much more useful. Somewhere in your code is, in this case, a global function called myFunc:
myFunc(data)
{
alert("The answer to life, the universe, and everything is: " + data.answer);
}
That's it. That's the "magic" of JSONP. Then to build in a timeout check is very simple, like shown above. Make the request and immediately after, start a timeout. After X seconds, if your flag still hasn't been set, then the request timed out.

I know this question is a little old but I didn't see an answer that gives a simple solution to the problem so I figured I would share my 'simple' solution.
$.getJSON("example.json", function() {
console.log( "success" );
}).fail(function() {
console.log( "error" );
});
We can simply use the .fail() callback to check to see if an error occurred.
Hope this helps :)

If you collaborate with the provider, you could send another query string parameter being the function to callback when there's an error.
?callback=?&error=?
This is called JSONPE but it's not at all a defacto standard.
The provider then passes information to the error function to help you diagnose.
Doesn't help with comm errors though - jQuery would have to be updated to also callback the error function on timeout, as in Adam Bellaire's answer.

Seems like this is working now:
jQuery(document).ajaxError(function(event, request, settings){
alert("Error");
});

I use this to catch an JSON error
try {
$.getJSON(ajaxURL,callback).ajaxError();
} catch(err) {
alert("wow");
alert("Error : "+ err);
}
Edit: Alternatively you can get the error message also. This will let you know what the error is exactly. Try following syntax in catch block
alert("Error : " + err);

Mayby this works?
.complete(function(response, status) {
if (response.status == "404")
alert("404 Error");
else{
//Do something
}
if(status == "error")
alert("Error");
else{
//Do something
}
});
I dont know whenever the status goes in "error" mode. But i tested it with 404 and it responded

you ca explicitly handle any error number by adding this attribute in the ajax request:
statusCode: {
404: function() {
alert("page not found");
}
}
so, your code should be like this:
jQuery.ajax({
type: "GET",
statusCode: {
404: function() {
alert("page not found");
}
},
url: handlerURL,
dataType: "jsonp",
success: function(results){
alert("Success!");
},
error: function(XMLHttpRequest, textStatus, errorThrown){
alert("Error");
}
});
hope this helps you :)

I also posted this answer in stackoverflow - Error handling in getJSON calls
I know it's been a while since someone answerd here and the poster probably already got his answer either from here or from somewhere else. I do however think that this post will help anyone looking for a way to keep track of errors and timeouts while doing getJSON requests. Therefore below my answer to the question
The getJSON structure is as follows (found on http://api.jqueri.com):
$(selector).getJSON(url,data,success(data,status,xhr))
most people implement that using
$.getJSON(url, datatosend, function(data){
//do something with the data
});
where they use the url var to provide a link to the JSON data, the datatosend as a place to add the "?callback=?" and other variables that have to be send to get the correct JSON data returned, and the success funcion as a function for processing the data.
You can however add the status and xhr variables in your success function. The status variable contains one of the following strings : "success", "notmodified", "error", "timeout", or "parsererror", and the xhr variable contains the returned XMLHttpRequest object
(found on w3schools)
$.getJSON(url, datatosend, function(data, status, xhr){
if (status == "success"){
//do something with the data
}else if (status == "timeout"){
alert("Something is wrong with the connection");
}else if (status == "error" || status == "parsererror" ){
alert("An error occured");
}else{
alert("datatosend did not change");
}
});
This way it is easy to keep track of timeouts and errors without having to implement a custom timeout tracker that is started once a request is done.
Hope this helps someone still looking for an answer to this question.

Error or fail not being reached when Ajax fails to fetch JSON

I am working on below Ajax code in JavaScript, I am trying to pop up a dialog box when the URL could not load the JSON properly the reason may be either expired token or incorrect token, in any case, I am expecting the code to hit the error or fail but it's not happening. When the URL could load the JSON successfully, success and complete blocks are being hit as expected but nothing is being hit when URL fails. I have tried to use async: false and tried to check with a boolean variable weHaveSuccess but console.log(weHaveSuccess); which is in the last line of the code is getting executing even before success/error is being executed and it seems to me like its still loading asynchronously. I would like to know why error block is not being hit when the JSON load from URL is getting failed.
My code
function checkUser(myURL, newAccessToken, weHaveSuccess) {
$.ajax({
type: "GET",
dataType: "jsonp",
async: false,
url: myURL + newAccessToken,
error: function (XMLHttpRequest, textStatus, errorThrown) {
console.log("Status: " + textStatus);
console.log("Error: " + errorThrown);
},
success: function (data) {
console.log("Hello 2 " + JSON.stringify(data));
weHaveSuccess = true;
console.log('Message from Success ' + weHaveSuccess);
},
complete: function () {
console.log('Message from Complete ' + weHaveSuccess);
}
}).done(function (data) {
alert("Success");
console.log(data);
}).fail(function (data) {
console.log(data);
alert("Failed");
}).always(function () {
alert("In Always");
});
console.log(weHaveSuccess);
}
Thanks in advance!

AJAX requests are asynchronous. It takes time for a remote request to be made and responded to. You will have to write your post-response code within the success function or call another function from there, not within the same scope as where the call is initiated.
I am taking a bit of a guess here about what your server returns on failure. An AJAX request success means simply that a 200 OK response was received, without any consideration of the contents of the data. If an error is simply a change in the data you will need do one of the following to show an error:
Have the server set a status code header on failure, perhaps 400 Bad Request.
In the success function look within your data for whatever error response you are expecting and trigger the alert() there.

First of all the console.log(weHaveSuccess); fires first, because the $.ajax() is asynchronous while console.log is not so ajax will be triggered and return the promise when finishes, but the browser will continue with the script.
In the jQuery ajax docs says:
Cross-domain requests and dataType: "jsonp" requests do not support
synchronous operation.
It's hard to debug without seeing the response, maybe you can add some info from the network or a URL?

How about if you try the following:
Add the jsonp setting to your $.ajax() function for the callback that will handle the response and console.log there:
function myCallback(data) {
console.log(data);
}
$.ajax({
type: "GET",
dataType: "jsonp",
jsonp: myCallback,
...

$.getJSON - ajax is sent but callback function is ignored - Internet Explorer

So here is my function
function ajax(addr,loading, loadTo, json){
addr = addr.replace(' ', '');
if (loading){
$("#"+loading).fadeIn();
}
if (json){
$.getJSON(addr, function(data){
alert('whoooo working'); // <--- it never goes here
if (loading){
$("#"+loading).fadeOut();
}
procJSON(data);
});
return true;
}
}
and I'm calling it with
var postid = $(this).attr('data-postid');
ajax(url+'tools/delete/'+postid, 'loading'+postid, false, true);
ajax is sent, image (loading image) is showed, but callback function is never called.
Isn't that just new reserved value from that IE's big list? Yes I know, IE is not a valid browser, but I can't blame my customers

As it fails in specific browsers, it's likely that it is a combination of unexpected headers in the response, and how the browser handles the data based on that.
If for example the response has the content type text/html instead of application/json, the browser might try to turn the response content into a HTML document (by adding pre tags around it), which would then cause the JSON parsing to fail.
If you use the $.ajax method, you can also catch any error message, which would give you a clue to what's going on:
$.ajax({
url: addr,
dataType: 'json',
success: function(data){
alert('whoooo working'); // <--- it never goes here
if (loading){
$("#"+loading).fadeOut();
}
procJSON(data);
},
error: function(o,c,m) { alert(m); }
});

How do I debug a jQuery Ajax request?

My code is:
var test = "it isn't working";
var response = $.ajax({
type: 'GET',
url: 'jquerydemo.php', //This is in the same site as the page calling this request, so it's not a same-domain error.
success: function(){
test = "it's working";
},
error: function(){
alert("Error detected");
}
}).responseText;
alert(test);
I tested the status code and it came out to a 200 and the error function never goes off, but neither does the success function. Like I said in my comment, it isn't a same-origin policy error. It just stays saying "it isn't working". What's going on here?

Try this:
error: function(jqXHR, textStatus, errorThrown) {
console.log(JSON.stringify(jqXHR));
console.log("AJAX error: " + textStatus + ' : ' + errorThrown);
}

Your ajax call is asynchronous. It has not completed yet when your alert at the end runs. Put an actual alert in the success function and you should see your result there.
Remember that making the ajax call just starts the asynchronous ajax call and then the rest of your code continues to run. In the code example you posted, that means your alert(test) call runs right away before the ajax call has completed.
You can ONLY examine the results of the ajax call from within the success handler itself.
var test = "it isn't working";
var response = $.ajax({
type: 'GET',
url: 'jquerydemo.php', //This is in the same site as the page calling this request, so it's not a same-domain error.
success: function(){
alert("it's working"); // put this here and you will see it
// if the ajax call is successful
},
error: function(){
alert("Error detected");
}
}).responseText;

To debug these types of things, I find Firebug an indispensable tool. It will show you exactly the response from the server (500 error, 553 error, what have you). You can put break points in your Javascript code and debug it step by step. Firebug works on Firefox.
For IE, you can use the Developer Tools feature which is similar to Firebug, specially on IE9 which seems more mature than previous versions of the Developer Tools for IE7 or IE8.

Move that alert(test) from end into the success function of the ajax call.
If it alerts it means code is working else it is not. you can only debug ajax call on its success return.
var test = "it isn't working";
var response = $.ajax({
type: 'GET',
url: 'jquerydemo.php',
success: function(){
test = "it's working";
alert(test); //It will alert when you ajax call returns successfully.
},
error: function(){
alert("Error detected");
}
}).responseText;
Hope this helps.

You can make it like
var response = $.ajax({
type: 'GET',
url: 'jquerydemo.php',
success: function(){
alert("it's working");
},
error: function(){
alert("Error detected");
}
}).responseText;
This will work....

jQuery $.getJSON not working

I am try to get a URL from a one server and using that URL to get contents of another server.
$.ajax({url : 'http://localhost:8080/geturl.jsp?A=1&B=2,C=3',
success : function (data)
{
alert(data);
$.getJSON(data, function (mydata)
{
alert(mydata);
});
},
error : function (data, status, xhr)
{
}
});
I know that we cannot make cross-domain requests in through ajax call, thats why i am using getJSON, i have the following problems
When i simply pass the data to the url part of getJSON (as shown in the code), the alert-box show the correct URL but no get request is being performed ( get requests were monitored from FireBug).
When a hard-code the data to be "http://www.google.com" then the get request is being performed but the no response comes, although the response headers comes and response code is 200 (but it was marked as RED in the Firebug (Dont know why :( )
When I tries to fetch a webpage host in localhost domain, then it is fetched correctly although the response was not JSON.
I have the following doubts
If the getJSON function accecpts only JSON objects as reponse then why no error came when perform above 3.
Whats the correct code to perform my the required functionality.
Suggestions to what happened in each case
Thanks in advance for the answers :)

The getJSON function can only be used across domains to fetch JSONP.
It does not magically evade any security restrictions.

http://api.jquery.com/jQuery.ajax/
This should be a working example for jsonp:
var request = jQuery.ajax(
{
url: "http://Your url",
success: function (data) { console.log('success!'); console.log(data); },
error: function (data) { console.log('error!'); console.log(data); },
dataType: "jsonp",
type: "GET",
data: { key: 'value' }
});