Here’s a useful debugging plugin for jQuery. It will list the handler/’s of any event binded to any element:

The Code:

// UPDATED -> NOW WORKS WITH jQuery 1.3.1
$.fn.listHandlers = function(events, outputFunction) {
    return this.each(function(i){
        var elem = this,
            dEvents = $(this).data('events');
        if (!dEvents) {return;}
        $.each(dEvents, function(name, handler){
            if((new RegExp('^(' + (events === '*' ? '.+' : events.replace(',','|').replace(/^on/i,'')) + ')$' ,'i')).test(name)) {
               $.each(handler, function(i,handler){
                   outputFunction(elem, '\n' + i + ': [' + name + '] : ' + handler );
               });
           }
        });
    });
};

Usage:

It’s pretty simple to use, you can specify the elements (as you usually would, via a selector), the events to be listed and the output function to which the plugin will feed the data.

If you’re using firebug then it’s best to use either the console.log function or console.info.

// List all onclick handlers of all anchor elements:
$('a').listHandlers('onclick', console.info);
 
// List all handlers for all events of all elements:
$('*').listHandlers('*', console.info);
 
// Write a custom output function:
$('#whatever').listHandlers('click',function(element,data){
    $('body').prepend('<br />' + element.nodeName + ': <br /><pre>' + data + '<\/pre>');
});

Note, this will only work if you’ve used jQuery’s native event registration methods, e.g. $(elem).click() / $(elem).bind('click').

Screenshot:

Screenshot of the plugin in action