Get event listeners attached to node using addEventListener

Question

I have already looked at these questions:

• How to find event listeners on a DOM node when debugging or from the JavaScript code?
• can I programmatically examine and modify Javascript event handlers on html elements?
• How to debug JavaScript/jQuery event bindings with Firebug (or similar tool)

however none of them answers how to get a list of event listeners attached to a node using addEventListener, without modifying the addEventListener prototype before the event listeners are created.

VisualEvent doesn't display all event listener (iphone specific ones) and I want to do this (somewhat) programmatically.

Answer 1

Chrome DevTools, Safari Inspector and Firebug support getEventListeners(node).

Answer 2

You can't.

The only way to get a list of all event listeners attached to a node is to intercept the listener attachment call.

DOM4 addEventListener

Says

Append an event listener to the associated list of event listeners with type set to type, listener set to listener, and capture set to capture, unless there already is an event listener in that list with the same type, listener, and capture.

Meaning that an event listener is added to the "list of event listeners". That's all. There is no notion of what this list should be nor how you should access it.

Answer 3

Since there is no native way to do this ,Here is the less intrusive solution i found (dont add any 'old' prototype methods):

var ListenerTracker=new function(){
    var targets=[];
    // listener tracking datas
    var _elements_  =[];
    var _listeners_ =[];
    this.init=function(){
        this.listen(Element,window);
    };
    this.listen=function(){
        for(var i=0;i<arguments.length;i++){
            if(targets.indexOf(arguments[i])===-1){
                targets.push(arguments[i]);//avoid duplicate call
                intercep_events_listeners(arguments[i]);
            }
        }
    };
    // register individual element an returns its corresponding listeners
    var register_element=function(element){
        if(_elements_.indexOf(element)==-1){
            // NB : split by useCapture to make listener easier to find when removing
            var elt_listeners=[{/*useCapture=false*/},{/*useCapture=true*/}];
            _elements_.push(element);
            _listeners_.push(elt_listeners);
        }
        return _listeners_[_elements_.indexOf(element)];
    };
    var intercep_events_listeners = function(target){
        var _target=target;
        if(target.prototype)_target=target.prototype;
        if(_target.getEventListeners)return;
        if(typeof(_target.addEventListener)!=='function'||typeof(_target.removeEventListener)!=='function'){
            console.log('target=',target);
            throw('\nListenerTracker Error:\nUnwrappable target.');
        }
        // backup overrided methods
        var _super_={
            "addEventListener"      : _target.addEventListener,
            "removeEventListener"   : _target.removeEventListener
        };

        _target["addEventListener"]=function(type, listener, useCapture){
            var listeners=register_element(this);
            // add event before to avoid registering if an error is thrown
            _super_["addEventListener"].apply(this,arguments);
            // adapt to 'elt_listeners' index
            var uc=(typeof(useCapture)==='object'?useCapture.useCapture:useCapture)?1:0;
            if(!listeners[uc][type])listeners[uc][type]=[];
            listeners[uc][type].push({cb:listener,args:arguments});
        };
        _target["removeEventListener"]=function(type, listener, useCapture){
            var listeners=register_element(this);
            // add event before to avoid registering if an error is thrown
            _super_["removeEventListener"].apply(this,arguments);
            // adapt to 'elt_listeners' index
            useCapture=(typeof(useCapture)==='object'?useCapture.useCapture:useCapture)?1:0;
            if(!listeners[useCapture][type])return;
            var lid = listeners[useCapture][type].findIndex(obj=>obj.cb===listener);
            if(lid>-1)listeners[useCapture][type].splice(lid,1);
        };
        _target["getEventListeners"]=function(type){
            var listeners=register_element(this);
            // convert to listener datas list
            var result=[];
            for(var useCapture=0,list;list=listeners[useCapture];useCapture++){
                if(typeof(type)=="string"){// filtered by type
                    if(list[type]){
                        for(var id in list[type]){
                            result.push({
                                "type":type,
                                "listener":list[type][id].cb,
                                "args":list[type][id].args,
                                "useCapture":!!useCapture
                            });
                        }
                    }
                }else{// all
                    for(var _type in list){
                        for(var id in list[_type]){
                            result.push({
                                "type":_type,
                                "listener":list[_type][id].cb,
                                "args":list[_type][id].args,
                                "useCapture":!!useCapture
                            });
                        }
                    }
                }
            }
            return result;
        };
    };

}();


ListenerTracker.init();

EDIT

Suggestion from @mplungjan: modified to listen to wrappable targets (singleton|constructor). 'init' tracks Element and window .

exemple with other wrappable target:

ListenerTracker.listen(XMLHttpRequest);

Suggestion from @kodfire : You may get optionals arguments with the args property.

Answer 4

I can't find a way to do this with code, but in stock Firefox 64, events are listed next to each HTML entity in the Developer Tools Inspector as noted on MDN's Examine Event Listeners page and as demonstrated in this image:

Answer 5

You can obtain all jQuery events using $._data($('[selector]')[0],'events'); change [selector] to what you need.

There is a plugin that gather all events attached by jQuery called eventsReport.

Also i write my own plugin that do this with better formatting.

But anyway it seems we can't gather events added by addEventListener method. May be we can wrap addEventListener call to store events added after our wrap call.

It seems the best way to see events added to an element with dev tools.

But you will not see delegated events there. So there we need jQuery eventsReport.

UPDATE: NOW We CAN see events added by addEventListener method SEE RIGHT ANSWER TO THIS QUESTION.