We Keep Coding

Exporting jQuery event listeners [duplicate]

With jQuery you can bind functions to an event triggered on a DOM object using .bind() or one of the event handler helper functions.
jQuery have to store this internally somehow and I wonder if is it possible given a DOM object, to find out which events have been bound to the object, and access those functions etc. The desired return result could look something like this:
{
click: [function1, function2],
change: [function3],
blur: [function4, function5, function6]
}

jQuery 1.7 has stopped exposing the events in the regular data() function. You can still get them like this:
var elem = $('#someid')[0];
var data = jQuery.hasData( elem ) && jQuery._data( elem );
console.log(data.events);
Please note, that this only works for Events which have been bound using jQuery. AFAIK you there is no way to see all the events which have been bound using the regular DOM functions like addEventListener.
You can see them in the webkit inspector though: In the Elements tab navigate to the desired DOM node, on the right side select the "Event Listeners" drop down.

Edit: the method below works only in jQuery < 1.7
You can find a lot of interesting tips and tricks in this article: Things you may not know about jQuery.
It seems that jQuery uses data to store event handlers:
You can access all event handlers
bound to an element (or any object)
through jQuery’s event storage:
// List bound events:
console.dir( jQuery('#elem').data('events') );
// Log ALL handlers for ALL events:
jQuery.each($('#elem').data('events'), function(i, event){
jQuery.each(event, function(i, handler){
console.log( handler['handler'].toString() );
});
});
// You can see the actual functions which will occur
// on certain events; great for debugging!

Prepend event listener [duplicate]

Lets say I have a web app which has a page that may contain 4 script blocks - the script I write may be found in one of those blocks, but I do not know which one, that is handled by the controller.
I bind some onclick events to a button, but I find that they sometimes execute in an order I did not expect.
Is there a way to ensure order, or how have you handled this problem in the past?

If order is important you can create your own events and bind callbacks to fire when those events are triggered by other callbacks.
$('#mydiv').click(function(e) {
// maniplate #mydiv ...
$('#mydiv').trigger('mydiv-manipulated');
});
$('#mydiv').bind('mydiv-manipulated', function(e) {
// do more stuff now that #mydiv has been manipulated
return;
});
Something like that at least.

Dowski's method is good if all of your callbacks are always going to be present and you are happy with them being dependant on each other.
If you want the callbacks to be independent of each other, though, you could be to take advantage of bubbling and attach subsequent events as delegates to parent elements. The handlers on a parent elements will be triggered after the handlers on the element, continuing right up to the document. This is quite good as you can use event.stopPropagation(), event.preventDefault(), etc to skip handlers and cancel or un-cancel the action.
$( '#mybutton' ).click( function(e) {
// Do stuff first
} );
$( '#mybutton' ).click( function(e) {
// Do other stuff first
} );
$( document ).delegate( '#mybutton', 'click', function(e) {
// Do stuff last
} );
Or, if you don't like this, you could use Nick Leaches bindLast plugin to force an event to be bound last: https://github.com/nickyleach/jQuery.bindLast.
Or, if you are using jQuery 1.5, you could also potentially do something clever with the new Deferred object.

I had been trying for ages to generalize this kind of process, but in my case I was only concerned with the order of first event listener in the chain.
If it's of any use, here is my jQuery plugin that binds an event listener that is always triggered before any others:
** UPDATED inline with jQuery changes (thanks Toskan) **
(function($) {
$.fn.bindFirst = function(/*String*/ eventType, /*[Object])*/ eventData, /*Function*/ handler) {
var indexOfDot = eventType.indexOf(".");
var eventNameSpace = indexOfDot > 0 ? eventType.substring(indexOfDot) : "";
eventType = indexOfDot > 0 ? eventType.substring(0, indexOfDot) : eventType;
handler = handler == undefined ? eventData : handler;
eventData = typeof eventData == "function" ? {} : eventData;
return this.each(function() {
var $this = $(this);
var currentAttrListener = this["on" + eventType];
if (currentAttrListener) {
$this.bind(eventType, function(e) {
return currentAttrListener(e.originalEvent);
});
this["on" + eventType] = null;
}
$this.bind(eventType + eventNameSpace, eventData, handler);
var allEvents = $this.data("events") || $._data($this[0], "events");
var typeEvents = allEvents[eventType];
var newEvent = typeEvents.pop();
typeEvents.unshift(newEvent);
});
};
})(jQuery);
Things to note:
This hasn't been fully tested.
It relies on the internals of the jQuery framework not changing (only tested with 1.5.2).
It will not necessarily get triggered before event listeners that are bound in any way other than as an attribute of the source element or using jQuery bind() and other associated functions.

The order the bound callbacks are called in is managed by each jQuery object's event data. There aren't any functions (that I know of) that allow you to view and manipulate that data directly, you can only use bind() and unbind() (or any of the equivalent helper functions).
Dowski's method is best, you should modify the various bound callbacks to bind to an ordered sequence of custom events, with the "first" callback bound to the "real" event. That way, no matter in what order they are bound, the sequence will execute in the right way.
The only alternative I can see is something you really, really don't want to contemplate: if you know the binding syntax of the functions may have been bound before you, attempt to un-bind all of those functions and then re-bind them in the proper order yourself. That's just asking for trouble, because now you have duplicated code.
It would be cool if jQuery allowed you to simply change the order of the bound events in an object's event data, but without writing some code to hook into the jQuery core that doesn't seem possible. And there are probably implications of allowing this that I haven't thought of, so maybe it's an intentional omission.

Please note that in the jQuery universe this must be implemented differently as of version 1.8. The following release note is from the jQuery blog:
.data(“events”): jQuery stores its event-related data in a data object
named (wait for it) events on each element. This is an internal data
structure so in 1.8 this will be removed from the user data name space
so it won’t conflict with items of the same name. jQuery’s event data
can still be accessed via jQuery._data(element, "events")
We do have complete control of the order in which the handlers will execute in the jQuery universe. Ricoo points this out above. Doesn't look like his answer earned him a lot of love, but this technique is very handy. Consider, for example, any time you need to execute your own handler prior to some handler in a library widget, or you need to have the power to cancel the call to the widget's handler conditionally:
$("button").click(function(e){
if(bSomeConditional)
e.stopImmediatePropagation();//Don't execute the widget's handler
}).each(function () {
var aClickListeners = $._data(this, "events").click;
aClickListeners.reverse();
});

function bindFirst(owner, event, handler) {
owner.unbind(event, handler);
owner.bind(event, handler);
var events = owner.data('events')[event];
events.unshift(events.pop());
owner.data('events')[event] = events;
}

just bind handler normally and then run:
element.data('events').action.reverse();
so for example:
$('#mydiv').data('events').click.reverse();

You can try something like this:
/**
* Guarantee that a event handler allways be the last to execute
* #param owner The jquery object with any others events handlers $(selector)
* #param event The event descriptor like 'click'
* #param handler The event handler to be executed allways at the end.
**/
function bindAtTheEnd(owner,event,handler){
var aux=function(){owner.unbind(event,handler);owner.bind(event,handler);};
bindAtTheStart(owner,event,aux,true);
}
/**
* Bind a event handler at the start of all others events handlers.
* #param owner Jquery object with any others events handlers $(selector);
* #param event The event descriptor for example 'click';
* #param handler The event handler to bind at the start.
* #param one If the function only be executed once.
**/
function bindAtTheStart(owner,event,handler,one){
var eventos,index;
var handlers=new Array();
owner.unbind(event,handler);
eventos=owner.data("events")[event];
for(index=0;index<eventos.length;index+=1){
handlers[index]=eventos[index];
}
owner.unbind(event);
if(one){
owner.one(event,handler);
}
else{
owner.bind(event,handler);
}
for(index=0;index<handlers.length;index+=1){
owner.bind(event,ownerhandlers[index]);
}
}

I have same issue and found this topic. the above answers can solve those problem, but I don't think them are good plans.
let us think about the real world.
if we use those answers, we have to change our code. you have to change your code style. something like this:
original:
$('form').submit(handle);
hack:
bindAtTheStart($('form'),'submit',handle);
as time goes on, think about your project. the code is ugly and hard to read! anthoer reason is simple is always better. if you have 10 bindAtTheStart, it may no bugs. if you have 100 bindAtTheStart, are you really sure you can keep them in right order?
so if you have to bind same events multiple.I think the best way is control js-file or js-code load order. jquery can handle event data as queue. the order is first-in, first-out. you don't need change any code. just change load order.

Here's my shot at this, covering different versions of jQuery:
// Binds a jQuery event to elements at the start of the event chain for that type.
jQuery.extend({
_bindEventHandlerAtStart: function ($elements, eventType, handler) {
var _data;
$elements.bind(eventType, handler);
// This bound the event, naturally, at the end of the event chain. We
// need it at the start.
if (typeof jQuery._data === 'function') {
// Since jQuery 1.8.1, it seems, that the events object isn't
// available through the public API `.data` method.
// Using `$._data, where it exists, seems to work.
_data = true;
}
$elements.each(function (index, element) {
var events;
if (_data) {
events = jQuery._data(element, 'events')[eventType];
} else {
events = jQuery(element).data('events')[eventType];
}
events.unshift(events.pop());
if (_data) {
jQuery._data(element, 'events')[eventType] = events;
} else {
jQuery(element).data('events')[eventType] = events;
}
});
}
});

In some special cases, when you cannot change how the click events are bound (event bindings are made from others' codes), and you can change the HTML element, here is a possible solution (warning: this is not the recommended way to bind events, other developers may murder you for this):
<span onclick="yourEventHandler(event)">Button</span>
With this way of binding, your event hander will be added first, so it will be executed first.

JQuery 1.5 introduces promises, and here's the simplest implementation I've seen to control order of execution. Full documentation at http://api.jquery.com/jquery.when/
$.when( $('#myDiv').css('background-color', 'red') )
.then( alert('hi!') )
.then( myClickFunction( $('#myID') ) )
.then( myThingToRunAfterClick() );

How do you force your Javascript event to run first, regardless of the order in which the events were added?

I have Javascript that people are including in their page. In my Javascript I have a version of jQuery (1.8 for sake of easy reference) that is sectioned off into its own namespace, and referenced via a global variable (but not one of the two default vars of "$" or "jQuery"). This allows users to have jQuery in their page and have it not interfere with the stuff I'm doing internally in my functions.
So we have one page that has jQuery already (1.4), and everything works fine, except that the user and my code are both listening to "click" events on elements, and theirs is going first, so on the few events they do that return false, jQuery stops propagation and my event never gets triggered. I need my event to go first. The user is expecting my onClick functionality to still work.
Now I know that jQuery keeps its own order of events internally through the _data() object, and through this it is possible to unbind existing events, bind my event, then rebind the existing events, but that only applies to objects bound through that instance of jQuery. I'd rather not just blindly look for the jQuery object in hopes that the conflict was introduced by a user's own version of jQuery. After all what happens when a user binds the event not through jQuery? Trying to manipulate the existing jQuery object in the page isn't a good solution.
I know that, depending on browser, they are using addEventListener/removeEventListener or attachEvent/detachEvent. If only I could get a listing of the already added events, I could rebind them in the order I wanted, but I can't find out how. Looking through the DOM via Chrome inspect I don't see onclick bound anywhere (not on the object, not on window or document either).
I'm having the darndest time trying to figure out just exactly where jQuery binds its listening. To be able to control the order of its own events, jQuery must blanketly listen somewhere and then fire off its own functions right? If I could figure out where that's done I might get some insight into how to ensure my event is always first. Or maybe there's some Javascript API I haven't been able to find on Google.
Any suggestions?

We solved this by just adding a little jQuery extension that inserts events at the head of the event chain:
$.fn.bindFirst = function(name, fn) {
var elem, handlers, i, _len;
this.bind(name, fn);
for (i = 0, _len = this.length; i < _len; i++) {
elem = this[i];
handlers = jQuery._data(elem).events[name.split('.')[0]];
handlers.unshift(handlers.pop());
}
};
Then, to bind your event:
$(".foo").bindFirst("click", function() { /* Your handler */ });
Easy peasy!

As Bergi and Chris Heald said in the comments, it turns out there's no way to get at the existing events from the DOM, and no method to insert events "first". They are fired in the order they were inserted by design, and hidden by design. As a few posters mentioned you have access to the ones added through the same instance of jQuery that you're using via jQuery's data, but that's it.
There is one other case where you can run before an event that was bound before your code ran, and that's if they used the "onclick" HTML attribute. In that case you can write a wrapper function, as nothingisnecessary pointed out in a rather over-the-top toned comment below. While this wouldn't help in the instance of the original question I asked, and it's now very rare for events to be bound this way (most people and frameworks use addEvent or attachEventListener underneath now), it is one scenario in which you can solve the issue of "running first", and since a lot of people visit this question looking for answers now, I thought I'd make sure the answer is complete.

I encounter an opposite situation where I was asked to include a library, which uses event.stopImmediatePropagation() on an element, to our website. So some of my event handlers are skipped. Here is what I do (as answered here):
<span onclick="yourEventHandler(event)">Button</span>
Warning: this is not the recommended way to bind events, other developers may murder you for this.

Its not a proper solution, but ... You can add event handler to parent node in capture phase. Not on target element itself!
<div>
<div id="target"></div>
</div>
target.parentNode.addEventListener('click',()=>{console.log('parent capture phase handler')},true)
Third argument in addEventListener means:
true - capture phase
false - bubble phase
Helpful links:
https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener
https://javascript.info/bubbling-and-capturing

Found it easiest to add addListener and removeListener methods to document (as that's only where I need them - I suppose you can use Element.prototype and this instead). Only one "real" listener is added per type, and it's just a func to call the actual listeners in order. The eventListeners dictionary is added to document (so can mess with the handler or order).
[edit]
I think the correct answer for most cases is to use the 3rd argument of addEventListener: https://stackoverflow.com/a/29923421. The answer below ignores the argument (on purpose).
[edit] Updated code to only add one extra property: document.eventHandlers + modified naming.
// Storage.
document.eventListeners = {}; // { type: [ handlerFunc, listenerFuncs ] }
// Add event listener - returns index.
document.addListener = (type, listener, atIndex) => {
// Get info.
const listening = document.eventListeners[type];
// Add to existing.
if (listening) {
// Clean up.
atIndex = atIndex || 0;
const listeners = listening[1]; // Array of funcs.
// Already has.
const iExists = listeners.indexOf(listener);
if (iExists !== -1) {
// Nothing to do.
if (iExists === atIndex)
return atIndex;
// Remove from old position.
listeners.splice(atIndex, 1);
}
// Add (supporting one cycle of negatives).
const nListeners = listeners.length;
if (atIndex > nListeners)
atIndex = nListeners;
else if (atIndex < 0)
atIndex = Math.max(0, atIndex + nListeners + 1);
listeners.splice(atIndex, 0, listener);
}
// New one.
else {
// Handler func.
const handler = (...args) => {
const listening = document.eventListeners[type];
if (listening) {
const listeners = listening[1]; // Array of funcs.
for (const listener of listeners)
listener(...args);
}
};
// Update dictionary.
document.eventListeners[type] = [ handler, [ listener ] ];
// Add listener.
document.addEventListener(type, handler);
// First one.
atIndex = 0;
}
// Return index.
return atIndex;
};
// Remove event listener - returns index (-1 if not found).
document.removeListener = (type, listener) => {
// Get info.
const listening = document.eventListeners[type];
if (!listening)
return -1;
// Check if exists.
const listeners = listening[1];
const iExists = listeners.indexOf(listener);
if (iExists !== -1) {
// Remove listener.
listeners.splice(iExists, 1);
// If last one.
if (!listeners.length) {
// Remove listener.
const handlerFunc = listening[0];
document.removeEventListener(type, handlerFunc);
// Update dictionary.
delete document.eventListeners[type];
}
}
// Return index.
return iExists;
}

Aliaksei Pavlenkos suggestion about useCapture can be used. His allegation that it must be attached to the parent node is wrong: MDN
Event listeners in the “capturing” phase are called before event listeners in any non-capturing phases
target.addEventListener(type, listener, useCapture);

Just so it's said, I think this might be possible if you override the native implementations of these functions. This is BAD practice - very bad practice when developing a library to alter native implementations, because it can easily conflict with other libraries.
However, for completeness, here's one possibility (completely untested, just demonstrating the general concept):
// override createElement()
var temp = document.createElement;
document.createElement = function() {
// create element
var el = document.createElement.original.apply(document, arguments);
// override addEventListener()
el.addEventListenerOriginal = el.addEventListener;
el._my_stored_events = [];
// add custom functions
el.addEventListener = addEventListenerCustom;
el.addEventListenerFirst = addEventListenerFirst;
// ...
};
document.createElement.original = temp;
// define main event listeners
function myMainEventListeners(type) {
if (myMainEventListeners.all[type] === undefined) {
myMainEventListeners.all[type] = function() {
for (var i = 0; i < this._my_stored_events.length; i++) {
var event = this._my_stored_events[i];
if (event.type == type) {
event.listener.apply(this, arguments);
}
}
}
}
return myMainEventListeners.all[type];
}
myMainEventListeners.all = {};
// define functions to mess with the event list
function addEventListenerCustom(type, listener, useCapture, wantsUntrusted) {
// register handler in personal storage list
this._my_stored_events.push({
'type' : type,
'listener' : listener
});
// register custom event handler
if (this.type === undefined) {
this.type = myMainEventListeners(type);
}
}
function addEventListenerFirst(type, listener) {
// register handler in personal storage list
this._my_stored_events.push({
'type' : type,
'listener' : listener
});
// register custom event handler
if (this.type === undefined) {
this.type = myMainEventListeners(type);
}
}
// ...
A lot more work would need to be done in this regard to truly lock this down, and again, it's best not to modify native libraries. But it's a useful mental exercise that helps to demonstrate the flexibility JavaScript provides in solving problems like this.

JavaScript - how to check if event already added

I want to add an listener exactly once for beforeunload. This is my pseudocode:
if(window.hasEventListener('beforeunload') === false) {
window.addEventListener('beforeunload', function() { ... }, false);
}
But hasEventListener does not exist obviously. How can I achieve this? Thanks.

In fact there is no need to check if an listener was added to a target:
If multiple identical EventListeners are registered on the same EventTarget with the same parameters, the duplicate instances are discarded. They do not cause the EventListener to be called twice, and since the duplicates are discarded, they do not need to be removed manually with the removeEventListener method.
Source:https://developer.mozilla.org/en-US/docs/Web/API/EventTarget.addEventListener#Multiple_identical_event_listeners

Using jquery you can do use data("events") on any object (here the window) :
var hasbeforeunload = $(window).data("events") && $(window).data("events").['beforeunload'];
But this works only for jquery added events.
In a more general case, you should simply store the information that you add a listener somewhere :
var addedListeners = {};
function addWindowListenerIfNone(eventType, fun) {
if (addedListeners[eventType]) return;
addedListeners[eventType] = fun;
window.addEventListener(eventType, fun);
}
I think there is no standard way in javascript to get the existing event handlers. At best you could surcharge the addEventListener function of Node to intercept and store the listeners but I don't recommend it...
EDIT :
From jQuery 1.8, event data are available in $._data(element, "events"). The change log has a warning that should be taken into account :
Note that this is not a supported public interface; the actual data
structures may change incompatibly from version to version.

In Chrome Dev tool, you can check all events attached to an element (For debugging)-
// print all events attached to document
var eventObjectAttachedToDocument = getEventListeners(document);
for (var event in eventObjectAttachedToDocument) {
console.log(event);
}

Trigger code when custom event is being bound in jQuery

JQuery has great support for custom events - .bind("foo", function(e).... However what if the mechanic of triggering the event is not ready yet and has to be constructed only on those elements that have the event bound on?
For example I want a scrollin event that gets fired when an element is scrolled into a viewport. To do this, I would onscroll have to check all the elements and trigger scrollin on those that were outside the viewport and now are inside. This is not acceptable.
There are some tricks to speed it up. For example one of the plugins for this checks all the elements in "private" $.cache and does the checking only on those that have scrollin event bound.
But that's also ugly. What I need is an additional callback for the binding of the event (additional to the callback for handling) that would take care of the scroll management, that is to put the element(s) into some elementsCheckOnScrol cache array.
I'm looking for something like:
$.delegateBind("scrollin", function(jqSelection) { ... });
element.bind("scrollin", function(e) {..}); //Calls ^ after internal bind management
Edit: This would be nice api!
$.bind("bind", function(onWhat) { ... })
:-)

If I'm not misunderstanding you, you could patch the bind method like this:
(function($) {
var oldBind = $.fn.bind;
$.fn.bind = function(name) {
if(name === "scrollin") {
delegateFunction(this);
}
oldBind.apply(this, arguments);
};
})(jQuery);
What it does is checking whether a scrollin is being bound, and if so, calls your delegate function. After that it simply calls the original bind function which does all jQuery things like it does regularly.
After having added this code, you could use it like this: http://jsfiddle.net/pimvdb/g4k2G/.
function delegateFunction(selection) {
alert(selection.length);
}
$('a').bind('scrollin', function() {});
Note that this does not support object literals being passed to .bind (only (name, func)), but you could implement that as well.

I found an $.event.special API, but I don't know "how much" public it is. It is not in the docs and has been changed at least once before. http://benalman.com/news/2010/03/jquery-special-events/