Listen for all events in JavaScript

Question

I'm trying to figure out how to listen for all events on a JavaScript object.

I know that I can add individual events with something like this

element.addEventListener("click", myFunction);
element.addEventListener("mouseover", myFunction);
...

I'm trying to figure out if there is a catch-all, I'd like to do something like this:

// Begin pseudocode
var myObj = document.getElementById('someID');

myObj.addEventListener(/*catch all*/, myFunction);

function myFunction() {
  alert(/*event name*/);
}
// End pseudocode

Answer 1

A more modern rewrite of @roman-bekkiev's answer:

Object.keys(window).forEach(key => {
    if (/^on/.test(key)) {
        window.addEventListener(key.slice(2), event => {
            console.log(event);
        });
    }
});

Here is an example to further customize event filtering:

/^on(key|mouse)/.test(key)

Answer 2

To pick up standard element's events.

var myObj = document.getElementById('someID')
for (var key in myObj) {
    if (key.search('on') === 0) {
       myObj.addEventListener(key.slice(2), myFunction)
    }
}

But as @jeremywoertink mentioned any other events are also possible...

Answer 3

I hate that this problem persists without a native or elegant solution.

A Better Solution?

This allows you to subscribe to a single CustomEvent for any EventTarget using target.addEventListener('*', ...).

    clear();

    /**
     * @param : source := EventTarget
     *  *   EventTarget.prototype
     *  *   Node (Element, Attr, etc)
     * @usage : [Node].addEventListener('*', ({ detail: e }) => {...}, false);
     */
    function proxyEventTargetSource(source) {
        var emit = source.dispatchEvent;  // obtain reference

        function proxy(event) {
            var { type } = event, any = new CustomEvent('*', { detail: event });  // use original event as detail
            if (!{ '*': true }[ type ]) emit.call(this, any);  // only emit "any" if type is not any.type ('*')
            return emit.call(this, event);
        }

        if ({ 'dispatchEvent': true }[ emit.name ]) source.dispatchEvent = proxy;  // attempt overwrite only if not already set (avoid rewrapping)
        return (source.dispatchEvent === proxy);  // indicate if its set after we try to
    }

    // proxyEventTargetSource(EventTarget.prototype);  // all targets
    proxyEventTargetSource(document);  // single target
    var e = new CustomEvent('any!', { detail: true });
    document.addEventListener('*', (e) => console.log('type: %s, original: %s, e: %O', e.type, e.detail.type, e), false);
    document.dispatchEvent(e);

Granted, a more native or [perhaps] more elegant way would be to use a native Proxy on apply for the target's dispatchEvent method, but that would maybe convey less for the sake of this post.

Gist: https://gist.github.com/cScarlson/875a9fca7ab7084bb608fb66adff0463

Known Issues

Apparently, this only works while driving event-dispatching through EventTargets's dispatchEvent method. That is, naturally triggering events through mouse events (for instance) does not work. There would need to be a way to wrap the internal method being called by natural event-triggers.

That being said, if you have a way around this, please show what you have in another answer.

Answer 4

As far as I know, it's possible.

For all native events, we can retrieve a list of supported events by iterating over the target.onevent properties and installing our listener for all of them.

for (const key in target) {
    if(/^on/.test(key)) {
        const eventType = key.substr(2);
        target.addEventListener(eventType, listener);
    }
}

The only other way that events are emitted which I know of is via EventTarget.dispatchEvent, which every Node and thefore every Element inherits.
To listen for all these manually triggered events, we can proxy the dispatchEvent method globally and install our listener just-in-time for the event whose name we just saw ✨ ^^

const dispatchEvent_original = EventTarget.prototype.dispatchEvent;
EventTarget.prototype.dispatchEvent = function (event) {
    if (!alreadyListenedEventTypes.has(event.type)) {
        target.addEventListener(event.type, listener, ...otherArguments);
        alreadyListenedEventTypes.add(event.type);
    }
    dispatchEvent_original.apply(this, arguments);
};

function snippet

function addEventListenerAll(target, listener, ...otherArguments) {

    // install listeners for all natively triggered events
    for (const key in target) {
        if (/^on/.test(key)) {
            const eventType = key.substr(2);
            target.addEventListener(eventType, listener, ...otherArguments);
        }
    }

    // dynamically install listeners for all manually triggered events, just-in-time before they're dispatched ;D
    const dispatchEvent_original = EventTarget.prototype.dispatchEvent;
    function dispatchEvent(event) {
        target.addEventListener(event.type, listener, ...otherArguments);  // multiple identical listeners are automatically discarded
        dispatchEvent_original.apply(this, arguments);
    }
    EventTarget.prototype.dispatchEvent = dispatchEvent;
    if (EventTarget.prototype.dispatchEvent !== dispatchEvent) throw new Error(`Browser is smarter than you think!`);

}


// usage example
addEventListenerAll(window, (evt) => {
    console.log(evt.type);
});
document.body.click();
document.body.dispatchEvent(new Event('omg!', { bubbles: true }));


// usage example with `useCapture`
// (also receives `bubbles: false` events, but in reverse order)
addEventListenerAll(
    window,
    (evt) => { console.log(evt.type); },
    true
);
document.body.dispatchEvent(new Event('omfggg!', { bubbles: false }));

Answer 5

You could use EventEmitter2 which does wildcards. The problem with doing a catchall like you're talking about is that there are so many events, and you can create your own. You'd have to make an array of specifically which events you're talking about, iterate over that, and bind each one individually.

Answer 6

You should probably pick the events you want to listen to, put them into an array and iterate over each:

['click','mouseover'].forEach(function(ev) {
    el.addEventListener(ev, function() {
        console.log('event:', ev)
    })
})

Answer 7

//listening for all click events on the document
   document.addEventListener('click', function (event) {

    //filtering for only events that happen on elements that contain the class
    //view_btn.          
  if (event.target.classList.contains( 'view_btn' )){
//logging out the id of the element        
          var id_of_clicked_element = event.target.getAttribute("id"); //
          console.log("button clicked has is of " + id_of_clicked_element)

        }
    });