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

Question

Hey fellow jQuery lovers,

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);
        }
    });

});

Answer 1

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"&gt;
</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 2

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.