Question

So I was reading through the code on Malsup’s twitter plugin and I noticed he’d written his own method to handle jsonp but with timeouts and errors. I can only assume the built in jQuery method ‘getJSON’ doesn’t have this functionality even though it clearly works fine.

So, should I continue to use Malsups version in my projects where I’m making JSONP requests or just stick with jQuery’s method. I have emailed Malsup and Paul Irish to ask about why it was necessary to write this but I didn’t hear back. Can’t blame ’em really:)

$.getJSONP = function(s){
    s.dataType = 'jsonp';
    $.ajax(s);

    // figure out what the callback fn is
    var $script = $(document.getElementsByTagName('head')[0].firstChild);
    var url = $script.attr('src') || '';
    var cb = (url.match(/callback=(\w+)/) || [])[1];
    if (!cb) 
        return; // bail
    var t = 0, cbFn = window[cb];

    $script[0].onerror = function(e){
        $script.remove();
        handleError(s, {}, "error", e);
        clearTimeout(t);
    };

    if (!s.timeout) 
        return;

    window[cb] = function(json){
        clearTimeout(t);
        cbFn(json);
        cbFn = null;
    };

    t = setTimeout(function(){
        $script.remove();
        handleError(s, {}, "timeout");
        if (cbFn) 
            window[cb] = function(){
            };
    }, s.timeout);

    function handleError(s, o, msg, e){
        // support jquery versions before and after 1.4.3
        ($.ajax.handleError || $.handleError)(s, o, msg, e);
    }
};

Answer 1

From the jQuery docs for getJSON(…)

Important: As of jQuery 1.4, if the
JSON file contains a syntax error, the
request will usually fail silently.
Avoid frequent hand-editing of JSON
data for this reason. JSON is a
data-interchange format with syntax
rules that are stricter than those of
JavaScript’s object literal notation.
For example, all strings represented
in JSON, whether they are properties
or values, must be enclosed in
double-quotes. For details on the JSON
format, see http://json.org/.

Presumably, silent failure was not something they liked, hence the plugin. In your case, if you’re making JSONP requests and find yourself using the onError, or onTimeout methods, then keep the plugin. I’ve not had to use JSONP in any real capacity, but I would assume that error handling is always nice to have. In the link to the jQuery docs, there is good discussion on this towards the end of the comments