How to debug JavaScript / jQuery event bindings with Firebug or similar tools?

See How to find event listeners on a DOM node.

In a nutshell, assuming at some point an event handler is attached to your element (eg): $('#foo').click(function() { console.log('clicked!') });

You inspect it like so:

jQuery 1.3.x var clickEvents = $('#foo').data("events").click; jQuery.each(clickEvents, function(key, value) { console.log(value) // prints "function() { console.log('clicked!') }" })

jQuery 1.4.x var clickEvents = $('#foo').data("events").click; jQuery.each(clickEvents, function(key, handlerObj) { console.log(handlerObj.handler) // prints "function() { console.log('clicked!') }" })

See jQuery.fn.data (where jQuery stores your handler internally).

jQuery 1.8.x var clickEvents = $._data($('#foo')[0], "events").click; jQuery.each(clickEvents, function(key, handlerObj) { console.log(handlerObj.handler) // prints "function() { console.log('clicked!') }" })

---

There's a nice bookmarklet called Visual Event that can show you all the events attached to an element. It has color-coded highlights for different types of events (mouse, keyboard, etc.). When you hover over them, it shows the body of the event handler, how it was attached, and the file/line number (on WebKit and Opera). You can also trigger the event manually.

It can't find every event because there's no standard way to look up what event handlers are attached to an element, but it works with popular libraries like jQuery, Prototype, MooTools, YUI, etc.

---

You could use FireQuery. It shows any events attached to DOM elements in the Firebug's HTML tab. It also shows any data attached to the elements through $.data.

---

Here's a plugin which can list all event handlers for any given element/event:

$.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 );
               });
           }
        });
    });
};

Use it like this:

// 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>');
});

Src: (my blog) -> http://james.padolsey.com/javascript/debug-jquery-events-with-listhandlers/

---

The WebKit Developer Console (found in Chrome, Safari, etc.) lets you view attached events for elements.

More detail in this Stack Overflow question

---

Use $._data(htmlElement, "events") in jquery 1.7+;

ex:

$._data(document, "events") or $._data($('.class_name').get(0), "events")

---

As a colleague suggested, console.log > alert:

var clickEvents = $('#foo').data("events").click;
jQuery.each(clickEvents, function(key, value) {
    console.log(value);
})

---

jQuery stores events in the following:

$("a#somefoo").data("events")

Doing a console.log($("a#somefoo").data("events")) should list the events attached to that element.

---

Using DevTools in the latest Chrome (v29) I find these two tips very helpful for debugging events:

Listing jQuery events of the last selected DOM element Inspect an element on the page type the following in the console: $._data($0, "events") //assuming jQuery 1.7+ It will list all jQuery event objects associated with it, expand the interested event, right-click on the function of the "handler" property and choose "Show function definition". It will open the file containing the specified function. Utilizing the monitorEvents() command

---

Looks like FireBug crew is working on an EventBug extension. It will add another panel to FireBug - Events.

"The events panel will list all of the event handlers on the page grouped by event type. For each event type you can open up to see the elements the listeners are bound to and summary of the function source." EventBug Rising

Although they cannot say right now when it will be released.

---

I also found jQuery Debugger in the chrome store. You can click on a dom item and it will show all events bound to it along with the callback function. I was debugging an application where events weren't being removed properly and this helped me track it down in minutes. Obviously this is for chrome though, not firefox.

---

ev icon next to elements

Within the Firefox Developer Tools' Inspector panel lists all events bound to an element.

First select an element with Ctrl + Shift + C, e.g. Stack Overflow's upvote arrow.

Click on the ev icon to the right of the element, and a dialogue opens:

https://i.stack.imgur.com/9QYSA.png

Click on the pause sign || symbol for the event you want, and this opens the debugger on the line of the handler.

You can now place a breakpoint there as usual in the debugger, by clicking on the left margin of the line.

This is mentioned at: https://developer.mozilla.org/en-US/docs/Tools/Page_Inspector/How_to/Examine_event_listeners

Unfortunately, I couldn't find a way for this to play nicely with prettyfication, it just seems to open at the minified line: How to beautify Javascript and CSS in Firefox / Firebug?

Tested on Firefox 42.

---

According to this thread, there is no way in Firebug to view what events are attached to listeners on a DOM element.

It looks like the best you can do is either what tj111 suggests, or you could right-click the element in the HTML viewer, and click "Log Events" so you can see which events are firing for a particular DOM element. I suppose one could do that to see what events could be firing off particular functions.

---

With version 2.0 Firebug introduced an Events panel, which lists all events for the element currently selected within the HTML panel.

https://i.stack.imgur.com/p9fUo.png

It can also display event listeners wrapped into jQuery event bindings in case the option Show Wrapped Listeners is checked, which you can reach via the Events panel's options menu.

With that panel the workflow to debug an event handler is as follows:

Select the element with the event listener you want to debug Inside the Events side panel right-click the function under the related event and choose Set Breakpoint Trigger the event

=> The script execution will stop at the first line of the event handler function and you can step debug it.

---

Firebug 2 does now incorporate DOM events debugging / inspection.

---