Uncaught TypeError: Can not set propery 'FUNCTION_NAME' of undefined for widget implementation

Question

I am trying to develop a jQuery widget which can be embedded on any site. Following is the script code:

(function($) {
    var jQuery;
    if (window.jQuery === undefined || window.jQuery.fn.jquery !== '1.6.2')
    {
        var script_tag = document.createElement('script');
        script_tag.setAttribute("type","text/javascript");
        script_tag.setAttribute("src","http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js");
        script_tag.onload = scriptLoadHandler;
        script_tag.onreadystatechange = function () 
        { 
            if (this.readyState == 'complete' || this.readyState == 'loaded')
                scriptLoadHandler();
        };
        (document.getElementsByTagName("head")[0] || document.documentElement).appendChild(script_tag);
    }
    else 
    {
        jQuery = window.jQuery;
        main();
    }
    function scriptLoadHandler() 
    {
        jQuery = window.jQuery.noConflict(true);
        main();
    }
    function main() {
        jQuery(document).ready(function($) {
            var css = $("<link>", { rel: "stylesheet", type: "text/css", href: "http://mysite.com/my_css_path.css" });
            css.appendTo('head');
        });
        $.fn.fetchfeed = function(options) {
            var defaults = {
                //default params;
            };
            var opts = $.extend(defaults, options);

            var myURL = "http://mysite.com/"+opts.user+".json?";
            var params = "&callback=?"
            var jsonp_url = myURL + encodeURIComponent(params);

            $.getJSON(jsonp_url, function(data) {
                //build widget html
            })
            .error(function() {
                //show error
            });
        }
    }
})(jQuery);

And following is the code which need to be placed on User's site:

 <script id='mywidgetscript' src='http://my_site.com/javascripts/widget.js'></script>
 <div id='my-widget-container'></div>
 <script>$('#my-widget-container').fetchfeed({/*parameters*/});</script>

When I put this code on other site and try to load the widget it gives me the Uncaught TypeError: Can not set property 'fetchfeed' of undefined error and fails to load the widget. What could be wrong?

Surprisingly this widget code is working on my site on localhost!!!

Answer 1

Okay, after countless attempts I solved it and got to learn many things. Still I'm unclear about many things. Do correct me by editing this answer or please comment if you find anything wrong.

First $.fn was null (or value being passed to it was null/undefined). Reason, the script was getting executed after <script>$('#my-widget-container').fetchfeed({/*parameters*/});</script> being called. So .fetchfeed({...}) was undefined.

Then I moved the code in window.onload it gave me error can not call method fetchfeed on null. It must be because it was not getting the element (i.e. $('#my-widget-container')) also script was not able to recognize $.

Again after few tweaks making $.fn.fetchfeed to function fetchfeed() {...} gave me error undefined fetchfeed. This was because function fetchfeed was inside another function.

Also encoding &callback=? parameter gives Access-Control-Allow-Origin error. This should be passed in url as is.

After some research I modified the code as below and now working correctly.

function fetchfeed(options) {
    var o = options;
    var jQuery;
    if (window.jQuery === undefined || window.jQuery.fn.jquery !== '1.6.2')
    {
        var script_tag = document.createElement('script');
        script_tag.setAttribute("type","text/javascript");
        script_tag.setAttribute("src","http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js");
        script_tag.onload = scriptLoadHandler;
        script_tag.onreadystatechange = function () 
        { 
            if (this.readyState == 'complete' || this.readyState == 'loaded')
                scriptLoadHandler();
        };
        (document.getElementsByTagName("head")[0] || document.documentElement).appendChild(script_tag);
    }
    else 
    {
        jQuery = window.jQuery;
        ff(jQuery, o);
    }
    function scriptLoadHandler() 
    {
        jQuery = window.jQuery.noConflict(true);
        ff(jQuery, o);
    }
    function ff($, options) {
        var defaults = {
            ...
        };
        var opts = $.extend(defaults, options);

        var jsonp_url = "http://mysite.com/?callback=?";            
        $.getJSON(jsonp_url, function(data) {
            //success
        })
        .error(function() {
            //fail
        });
    }
}

Code on user's site/blog will be

<div id='my-widget-container'></div>
<script id='my_widget_script' src='https://PATH_OF_SCRIPT/FILE_NAME.js'></script>
<script type='text/javascript'>
    fetchfeed({/*params*/});
</script>

The function will be executed when page load completes.