jQuery ajax (jsonp) ignores a timeout and doesn't fire the error event

Question

To add some basic error handling, I wanted to rewrite a piece of code that used jQuery's $.getJSON to pull in some photo's from Flickr. The reason for doing this is that $.getJSON doesn't provide error handling or work with timeouts.

Since $.getJSON is just a wrapper around $.ajax I decided to rewrite the thing and surprise surprise, it works flawlessly.

Now the fun starts though. When I deliberately cause a 404 (by changing the URL) or cause the network to timeout (by not being hooked up to the interwebs), the error event doesn't fire, at all. I'm at a loss as to what I'm doing wrong. Help is much appreciated.

Here's the code:

$(document).ready(function(){

    // var jsonFeed = "http://api.flickr.com/services/feeds/photos_public.gne"; // correct URL
    var jsonFeed = "http://api.flickr.com/services/feeds/photos_public.gne_______"; // this should throw a 404

    $.ajax({
        url: jsonFeed,
        data: { "lang" : "en-us",
                "format" : "json",
                "tags" : "sunset"
        },
        dataType: "jsonp",
        jsonp: "jsoncallback",
        timeout: 5000,
        success: function(data, status){
            $.each(data.items, function(i,item){
                $("<img>").attr("src", (item.media.m).replace("_m.","_s."))
                          .attr("alt", item.title)
                          .appendTo("ul#flickr")
                          .wrap("<li><a href=\"" + item.link + "\"></a></li>");
                if (i == 9) return false;
            });
        },
        error: function(XHR, textStatus, errorThrown){
            alert("ERREUR: " + textStatus);
            alert("ERREUR: " + errorThrown);
        }
    });

});

I'd like to add that this question was asked when jQuery was at version 1.4.2

Answer 1

jQuery 1.5 and higher have better support for error handling with JSONP requests. However, you need to use the $.ajax method instead of $.getJSON. For me, this works:

var req = $.ajax({
    url : url,
    dataType : "jsonp",
    timeout : 10000
});

req.success(function() {
    console.log('Yes! Success!');
});

req.error(function() {
    console.log('Oh noes!');
});

The timeout seems to do the trick and call the error handler, when there is no successful request after 10 seconds.

I did a little blogpost on this subject as well.

Answer 2

This is a known limitation with the native jsonp implementation in jQuery. The text below is from IBM DeveloperWorks

JSONP is a very powerful technique for building mashups, but, unfortunately, it is not a cure-all for all of your cross-domain communication needs. It has some drawbacks that must be taken into serious consideration before committing development resources. First and foremost, there is no error handling for JSONP calls. If the dynamic script insertion works, you get called; if not, nothing happens. It just fails silently. For example, you are not able to catch a 404 error from the server. Nor can you cancel or restart the request. You can, however, timeout after waiting a reasonable amount of time. (Future jQuery versions may have an abort feature for JSONP requests.)

However there's a jsonp plug-in available on GoogleCode that provides support for error handling. To get started, just make the following changes to your code.

You can either download it, or just add a script reference to the plug-in.

<script type="text/javascript" 
     src="http://jquery-jsonp.googlecode.com/files/jquery.jsonp-1.0.4.min.js">
</script>

Then modify your ajax call as shown below:

$(function(){
    //var jsonFeed = "http://api.flickr.com/services/feeds/photos_public.gne"; // correct URL
    var jsonFeed = "http://api.flickr.com/services/feeds/photos_public.gne_______"; // this should throw a 404  
    $.jsonp({
        url: jsonFeed,
        data: { "lang" : "en-us",
                "format" : "json",
                "tags" : "sunset"
        },
        dataType: "jsonp",
        callbackParameter: "jsoncallback",
        timeout: 5000,
        success: function(data, status){
            $.each(data.items, function(i,item){
                $("<img>").attr("src", (item.media.m).replace("_m.","_s."))
                          .attr("alt", item.title)
                          .appendTo("ul#flickr")
                          .wrap("<li><a href=\"" + item.link + "\"></a></li>");
                if (i == 9) return false;
            });
        },
        error: function(XHR, textStatus, errorThrown){
            alert("ERREUR: " + textStatus);
            alert("ERREUR: " + errorThrown);
        }
    });
});

Answer 3

A solution if you're stuck with jQuery 1.4:

var timeout = 10000;
var id = setTimeout( errorCallback, timeout );
$.ajax({
    dataType: 'jsonp',
    success: function() {
        clearTimeout(id);
        ...
    }
});

Answer 4

This may be a "known" limitation of jQuery; however, it does not seem to be well documented. I spent about 4 hours today trying to understand why my timeout was not working.

I switched to jquery.jsonp and it worked liked a charm. Thank you.

Answer 5

Seems to be resolved as of jQuery 1.5. I've tried the code above and I get the callback.

I say "seems to be" because the documentation of the error callback for jQuery.ajax() still has the following note:

Note: This handler is not called for cross-domain script and JSONP requests.

Answer 6

The jquery-jsonp jQuery plugin mentioned in Jose Basilio's answer can now be found on GitHub.

Unfortunately the documentation is somewhat spartan, so I've provided a simple example:

    $.jsonp({
        cache: false,
        url: "url",
        callbackParameter: "callback",
        data: { "key" : "value" },
        success: function (json, textStatus, xOptions) {
            // handle success - textStatus is "success"   
        },
        error: function (xOptions, textStatus) {
            // handle failure - textStatus is either "error" or "timeout"
        }
    });

Important Include the callbackParameter in the call $.jsonp() otherwise I've found that the callback function never gets injected into the query string of the service call (current as of version 2.4.0 of jquery-jsonp).

I know this question is old, but the issue of error handling using JSONP is still not 'resolved'. Hopefully this update will assist others as this question is the top-ranked within Google for "jquery jsonp error handling".

Answer 7

What about listening to the script's onerror event ? I had this problem and solved it by patching jquery's method where the script tag was created. Here is the interesting bit of code :

// Attach handlers for all browsers
script.onload = script.onreadystatechange = function( _, isAbort ) {

    if ( isAbort || !script.readyState || /loaded|complete/.test( script.readyState ) ) {

        cleanup();

        // Callback if not abort
        if ( !isAbort ) {
            callback( 200, "success" );
        }
    }
};

/* ajax patch : */
script.onerror = function(){
    cleanup();

    // Sends an inappropriate error, still better than nothing
    callback(404, "not found");
};

function cleanup(){
    // Handle memory leak in IE
    script.onload = script.onreadystatechange = null;

    // Remove the script
    if ( head && script.parentNode ) {
        head.removeChild( script );
    }

    // Dereference the script
    script = undefined;
}

What do you think of this solution ? Is it likely to cause compatibility issues ?