So by default jQuery uses a HTML Dom Element as the calling object in a event callback
var el = $("#foo");
el.on("click", function()
{
// this will output a div element
console.log(this);
});
Is there a simple way to make it use the jQuery object as the calling function by default instead
so that "this" references the jQuery object and I don't have to wrap "this" in a jQuery constructor.
$("#foo").on("click", function()
{
// this will instead output the jQuery object el declared above
console.log(this);
this.addClass("fee").find(".roo").remove();
});
I want to avoid creating variable names and just use "this" to refer to the jQuery object that added the listener.
You can make your own handler which calls a function bound to the jQuery collection:
const onClick = (selector, callback) => {
const jQueryCollection = $(selector);
jQueryCollection.on('click', callback.bind(jQueryCollection));
};
onClick("#foo", function() {
this.addClass("fee").find(".roo").remove();
});
.fee {
background-color: yellow;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="foo">foo
</div>
Or, extend jQuery:
$.fn.onClickWithThis = function(callback) {
const jQueryCollection = $(this);
jQueryCollection.on('click', callback.bind(jQueryCollection));
};
$("#foo").onClickWithThis(function() {
this.addClass("fee").find(".roo").remove();
});
.fee {
background-color: yellow;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="foo">foo
</div>
I wanted to use a preexisting option if possible, but since there doesn't seem to be one.
I overwrote the on function instead.
Most of the credit to CertainPerformance, but this solution works best since it overwrites the callback and works with the 4 available parameters that on can take.
(function ($)
{
let originalOn = $.fn.on;
$.fn.on = function(...args)
{
for(let key in args)
{
if(typeof(args[key]) == "function")
{
let originalCallback = args[key];
args[key] = function(...args)
{
originalCallback.bind($(this))(...args);
}
}
}
originalOn.bind(this)(...args);
}
})($);
I am dynamically adding events using addEvent("keydown", function() {}); to an element. My problem is that there are times when this code get's run on the same element twice or more. The behavior becomes clunky as the function registered for that event runs a couple of times.
Is there a way for me to only run the code above only once on an element? Maybe check if the event has already been added before?
Either don't use a new function each time, or use a class or something to tell you you've added it.
Not using a new function each time
MooTools' addEvent is a fairly thin wrapper on addEventListener/attachEvent, which won't add the same function twice. So if you ensure you're using the same function, you can call addEvent again without it doing anything:
// Somewhere it's created **once**
function keyDownHandler() {
// ....
}
then:
element.addEvent("keydown", keyDownHandler); // Adds it only if not there
Live Example:
addIt();
addIt();
function addIt() {
$("foo").addEvent("click", handler);
}
function handler() {
var p = document.createElement('p');
p.innerHTML = new Date();
document.body.appendChild(p);
}
<div id="foo">Click me</div>
<script src="https://ajax.googleapis.com/ajax/libs/mootools/1.5.0/mootools-yui-compressed.js"></script>
Remembering you've added it:
if (!element.hasClass("keydown-handler")) {
element.addClass("keydown-handler").addEvent("keydown", function() { /*...*/});
}
Live Example:
addIt();
addIt();
function addIt() {
var element = $("foo");
if (!element.hasClass("click-handler")) {
element.addClass("click-handler").addEvent(
"click",
function() {
var p = document.createElement('p');
p.innerHTML = new Date();
document.body.appendChild(p);
}
);
}
}
<div id="foo">Click me</div>
<script src="https://ajax.googleapis.com/ajax/libs/mootools/1.5.0/mootools-yui-compressed.js"></script>
Maybe your problem is not where or when to add event handler, but how to add. It is possible to delegate events to parent element. For example, this is a classic way of adding an event handler directly to the target element.
new Element( 'p', { 'text': 'Some Text' } ).inject( $( 'container' ) );
$$( '#container p' ).addEvent( 'click', function() {
console.log( this );
});
new Element( 'p', { 'text': 'Some Text' } ).inject( $( 'container' ) );
And, of course, only the first paragraph has click event.
And below is an example of event delegation.
$( 'container' ).addEvent( 'click:relay(p)', function() {
console.log( this );
});
$( 'container' ).adopt([
new Element( 'p', { 'text': 'Some Text' } ),
new Element( 'p', { 'text': 'Some Text' } )
]);
Since event listener is assigned to a parent for all of its children, all paragraphs will have the click event, no matter when and where they are created. It is very useful when you are adding elements into the page dynamically.
I do not know how much this helps, but it's good to know.
Element.Delegation
I had the same problem initiating js class instance which should add event, so using 'document.addEventListener' made situation when code attached to listeners called multiple time after creating instances of the same class. I resolved it by static function added into class Helper:
'use strict';
export default class Helper {
//avoid multiple reactions for reinited objects which uses document attached events
static events = [];
static addSingleEventListener(event_name, instance, callback) {
if (!instance.instance_key) {
console.error(`Instance ${instance.constructor.name} not has instance_key field!`);
return;
}
if (!Helper.events[instance.instance_key]) {
Helper.events[instance.instance_key] = [];
}
if (!Helper.events[instance.instance_key][event_name]) {
Helper.events[instance.instance_key][event_name] = callback.bind(instance);
document.addEventListener(event_name, e => Helper.events[instance.instance_key][event_name](e));
} else {
Helper.events[instance.instance_key][event_name] = callback.bind(instance);
}
}
}
Using:
'use strict';
import Helper from './helper.js';
//16-11-2022
export default class Color {
constructor(panel) {
this.panel = panel;
this.instance_key = 'woof-sd-color';//!! for attaching document events
Helper.addSingleEventListener('woof_sd_childs_term_color', this, e => this.reload(parseInt(e.detail.id)));
}
}
Make your attention on this.instance_key - this should be defined and unique!
I would like to have something like:
$('#myDiv').bind('class "submission ok" added'){
alert('class "submission ok" has been added');
});
There is no event raised when a class changes. The alternative is to manually raise an event when you programatically change the class:
$someElement.on('event', function() {
$('#myDiv').addClass('submission-ok').trigger('classChange');
});
// in another js file, far, far away
$('#myDiv').on('classChange', function() {
// do stuff
});
UPDATE - 2015
This question seems to be gathering some visitors, so here is an update with an approach which can be used without having to modify existing code using the new MutationObserver:
var $div = $("#foo");
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(mutation) {
var attributeValue = $(mutation.target).prop(mutation.attributeName);
console.log("Class attribute changed to:", attributeValue);
});
});
observer.observe($div[0], {
attributes: true,
attributeFilter: ['class']
});
$div.addClass('red');
.red {
color: #C00;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
<div id="foo" class="bar">#foo.bar</div>
Be aware that the MutationObserver is only available for newer browsers, specifically Chrome 26, FF 14, IE 11, Opera 15 and Safari 6. See MDN for more details. If you need to support legacy browsers then you will need to use the method I outlined in my first example.
UPDATE - 2022
Here's an implementation of the above wrapped in to a jQuery extension method:
// extension method:
$.fn.classChange = function(cb) {
return $(this).each((_, el) => {
new MutationObserver(mutations => {
mutations.forEach(mutation => cb && cb(mutation.target, $(mutation.target).prop(mutation.attributeName)));
}).observe(el, {
attributes: true,
attributeFilter: ['class'] // only listen for class attribute changes
});
});
}
// usage:
const $foo = $("#foo").classChange((el, newClass) => console.log(`#${el.id} had its class updated to: ${newClass}`));
const $fizz = $("#fizz").classChange((el, newClass) => console.log(`#${el.id} had its class updated to: ${newClass}`));
// trigger
$('#trigger').on('click', () => {
$foo.removeClass('red');
$fizz.addClass('green dark-bg');
});
.red {
color: #C00;
}
.green {
color: #0C0;
}
.dark-bg {
background-color: #666;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
<button id="trigger">Change classes</button>
<div id="foo" class="bar red">#foo.bar</div>
<div id="fizz" class="buzz">#fizz.buzz</div>
You could replace the original jQuery addClass and removeClass functions with your own that would call the original functions and then trigger a custom event. (Using a self-invoking anonymous function to contain the original function reference)
(function( func ) {
$.fn.addClass = function() { // replace the existing function on $.fn
func.apply( this, arguments ); // invoke the original function
this.trigger('classChanged'); // trigger the custom event
return this; // retain jQuery chainability
}
})($.fn.addClass); // pass the original function as an argument
(function( func ) {
$.fn.removeClass = function() {
func.apply( this, arguments );
this.trigger('classChanged');
return this;
}
})($.fn.removeClass);
Then the rest of your code would be as simple as you'd expect.
$(selector).on('classChanged', function(){ /*...*/ });
Update:
JS Fiddle Demo
This approach does make the assumption that the classes will only be changed via the jQuery addClass and removeClass methods. If classes are modified in other ways (such as direct manipulation of the class attribute through the DOM element) use of something like MutationObservers as explained in the accepted answer here would be necessary.
Also as a couple improvements to these methods:
Trigger an event for each class being added (classAdded) or removed (classRemoved) with the specific class passed as an argument to the callback function and only triggered if the particular class was actually added (not present previously) or removed (was present previously)
Only trigger classChanged if any classes are actually changed
(function( func ) {
$.fn.addClass = function(n) { // replace the existing function on $.fn
this.each(function(i) { // for each element in the collection
var $this = $(this); // 'this' is DOM element in this context
var prevClasses = this.getAttribute('class'); // note its original classes
var classNames = $.isFunction(n) ? n(i, prevClasses) : n.toString(); // retain function-type argument support
$.each(classNames.split(/\s+/), function(index, className) { // allow for multiple classes being added
if( !$this.hasClass(className) ) { // only when the class is not already present
func.call( $this, className ); // invoke the original function to add the class
$this.trigger('classAdded', className); // trigger a classAdded event
}
});
if( prevClasses != this.getAttribute('class') ) $this.trigger('classChanged'); // trigger the classChanged event
});
return this; // retain jQuery chainability
}
})($.fn.addClass); // pass the original function as an argument
(function( func ) {
$.fn.removeClass = function(n) {
this.each(function(i) {
var $this = $(this);
var prevClasses = this.getAttribute('class');
var classNames = $.isFunction(n) ? n(i, prevClasses) : n.toString();
$.each(classNames.split(/\s+/), function(index, className) {
if( $this.hasClass(className) ) {
func.call( $this, className );
$this.trigger('classRemoved', className);
}
});
if( prevClasses != this.getAttribute('class') ) $this.trigger('classChanged');
});
return this;
}
})($.fn.removeClass);
With these replacement functions you can then handle any class changed via classChanged or specific classes being added or removed by checking the argument to the callback function:
$(document).on('classAdded', '#myElement', function(event, className) {
if(className == "something") { /* do something */ }
});
Use trigger to fire your own event. When ever you change class add trigger with name
JS Fiddle DEMO
$("#main").on('click', function () {
$("#chld").addClass("bgcolorRed").trigger("cssFontSet");
});
$('#chld').on('cssFontSet', function () {
alert("Red bg set ");
});
you can use something like this:
$(this).addClass('someClass');
$(Selector).trigger('ClassChanged')
$(otherSelector).bind('ClassChanged', data, function(){//stuff });
but otherwise, no, there's no predefined function to fire an event when a class changes.
Read more about triggers here
I'm using jQuery in my site and I would like to trigger certain actions when a certain div is made visible.
Is it possible to attach some sort of "isvisible" event handler to arbitrary divs and have certain code run when they the div is made visible?
I would like something like the following pseudocode:
$(function() {
$('#contentDiv').isvisible(function() {
alert("do something");
});
});
The alert("do something") code should not fire until the contentDiv is actually made visible.
Thanks.
You could always add to the original .show() method so you don't have to trigger events every time you show something or if you need it to work with legacy code:
Jquery extension:
jQuery(function($) {
var _oldShow = $.fn.show;
$.fn.show = function(speed, oldCallback) {
return $(this).each(function() {
var obj = $(this),
newCallback = function() {
if ($.isFunction(oldCallback)) {
oldCallback.apply(obj);
}
obj.trigger('afterShow');
};
// you can trigger a before show if you want
obj.trigger('beforeShow');
// now use the old function to show the element passing the new callback
_oldShow.apply(obj, [speed, newCallback]);
});
}
});
Usage example:
jQuery(function($) {
$('#test')
.bind('beforeShow', function() {
alert('beforeShow');
})
.bind('afterShow', function() {
alert('afterShow');
})
.show(1000, function() {
alert('in show callback');
})
.show();
});
This effectively lets you do something beforeShow and afterShow while still executing the normal behavior of the original .show() method.
You could also create another method so you don't have to override the original .show() method.
The problem is being addressed by DOM mutation observers. They allow you to bind an observer (a function) to events of changing content, text or attributes of dom elements.
With the release of IE11, all major browsers support this feature, check http://caniuse.com/mutationobserver
The example code is a follows:
$(function() {
$('#show').click(function() {
$('#testdiv').show();
});
var observer = new MutationObserver(function(mutations) {
alert('Attributes changed!');
});
var target = document.querySelector('#testdiv');
observer.observe(target, {
attributes: true
});
});
<div id="testdiv" style="display:none;">hidden</div>
<button id="show">Show hidden div</button>
<script type="text/javascript" src="https://code.jquery.com/jquery-1.9.1.min.js"></script>
There is no native event you can hook into for this however you can trigger an event from your script after you have made the div visible using the .trigger function
e.g
//declare event to run when div is visible
function isVisible(){
//do something
}
//hookup the event
$('#someDivId').bind('isVisible', isVisible);
//show div and trigger custom event in callback when div is visible
$('#someDivId').show('slow', function(){
$(this).trigger('isVisible');
});
You can use jQuery's Live Query plugin.
And write code as follows:
$('#contentDiv:visible').livequery(function() {
alert("do something");
});
Then everytime the contentDiv is visible, "do something" will be alerted!
redsquare's solution is the right answer.
But as an IN-THEORY solution you can write a function which is selecting the elements classed by .visibilityCheck (not all visible elements) and check their visibility property value; if true then do something.
Afterward, the function should be performed periodically using the setInterval() function. You can stop the timer using the clearInterval() upon successful call-out.
Here's an example:
function foo() {
$('.visibilityCheck').each(function() {
if ($(this).is(':visible')){
// do something
}
});
}
window.setInterval(foo, 100);
You can also perform some performance improvements on it, however, the solution is basically absurd to be used in action. So...
The following code (pulled from http://maximeparmentier.com/2012/11/06/bind-show-hide-events-with-jquery/) will enable you to use $('#someDiv').on('show', someFunc);.
(function ($) {
$.each(['show', 'hide'], function (i, ev) {
var el = $.fn[ev];
$.fn[ev] = function () {
this.trigger(ev);
return el.apply(this, arguments);
};
});
})(jQuery);
If you want to trigger the event on all elements (and child elements) that are actually made visible, by $.show, toggle, toggleClass, addClass, or removeClass:
$.each(["show", "toggle", "toggleClass", "addClass", "removeClass"], function(){
var _oldFn = $.fn[this];
$.fn[this] = function(){
var hidden = this.find(":hidden").add(this.filter(":hidden"));
var result = _oldFn.apply(this, arguments);
hidden.filter(":visible").each(function(){
$(this).triggerHandler("show"); //No bubbling
});
return result;
}
});
And now your element:
$("#myLazyUl").bind("show", function(){
alert(this);
});
You could add overrides to additional jQuery functions by adding them to the array at the top (like "attr")
a hide/show event trigger based on Glenns ideea:
removed toggle because it fires show/hide and we don't want 2fires for one event
$(function(){
$.each(["show","hide", "toggleClass", "addClass", "removeClass"], function(){
var _oldFn = $.fn[this];
$.fn[this] = function(){
var hidden = this.find(":hidden").add(this.filter(":hidden"));
var visible = this.find(":visible").add(this.filter(":visible"));
var result = _oldFn.apply(this, arguments);
hidden.filter(":visible").each(function(){
$(this).triggerHandler("show");
});
visible.filter(":hidden").each(function(){
$(this).triggerHandler("hide");
});
return result;
}
});
});
I had this same problem and created a jQuery plugin to solve it for our site.
https://github.com/shaunbowe/jquery.visibilityChanged
Here is how you would use it based on your example:
$('#contentDiv').visibilityChanged(function(element, visible) {
alert("do something");
});
What helped me here is recent ResizeObserver spec polyfill:
const divEl = $('#section60');
const ro = new ResizeObserver(() => {
if (divEl.is(':visible')) {
console.log("it's visible now!");
}
});
ro.observe(divEl[0]);
Note that it's crossbrowser and performant (no polling).
Just bind a trigger with the selector and put the code into the trigger event:
jQuery(function() {
jQuery("#contentDiv:hidden").show().trigger('show');
jQuery('#contentDiv').on('show', function() {
console.log('#contentDiv is now visible');
// your code here
});
});
Use jQuery Waypoints :
$('#contentDiv').waypoint(function() {
alert('do something');
});
Other examples on the site of jQuery Waypoints.
I did a simple setinterval function to achieve this. If element with class div1 is visible, it sets div2 to be visible. I know not a good method, but a simple fix.
setInterval(function(){
if($('.div1').is(':visible')){
$('.div2').show();
}
else {
$('.div2').hide();
}
}, 100);
You can also try jQuery appear plugin as mentioned in parallel thread https://stackoverflow.com/a/3535028/741782
This support easing and trigger event after animation done! [tested on jQuery 2.2.4]
(function ($) {
$.each(['show', 'hide', 'fadeOut', 'fadeIn'], function (i, ev) {
var el = $.fn[ev];
$.fn[ev] = function () {
var result = el.apply(this, arguments);
var _self=this;
result.promise().done(function () {
_self.triggerHandler(ev, [result]);
//console.log(_self);
});
return result;
};
});
})(jQuery);
Inspired By http://viralpatel.net/blogs/jquery-trigger-custom-event-show-hide-element/
There is a jQuery plugin available for watching change in DOM attributes,
https://github.com/darcyclarke/jQuery-Watch-Plugin
The plugin wraps All you need do is bind MutationObserver
You can then use it to watch the div using:
$("#selector").watch('css', function() {
console.log("Visibility: " + this.style.display == 'none'?'hidden':'shown'));
//or any random events
});
Hope this will do the job in simplest manner:
$("#myID").on('show').trigger('displayShow');
$('#myID').off('displayShow').on('displayShow', function(e) {
console.log('This event will be triggered when myID will be visible');
});
I changed the hide/show event trigger from Catalint based on Glenns idea.
My problem was that I have a modular application. I change between modules showing and hiding divs parents. Then when I hide a module and show another one, with his method I have a visible delay when I change between modules. I only need sometimes to liten this event, and in some special childs. So I decided to notify only the childs with the class "displayObserver"
$.each(["show", "hide", "toggleClass", "addClass", "removeClass"], function () {
var _oldFn = $.fn[this];
$.fn[this] = function () {
var hidden = this.find(".displayObserver:hidden").add(this.filter(":hidden"));
var visible = this.find(".displayObserver:visible").add(this.filter(":visible"));
var result = _oldFn.apply(this, arguments);
hidden.filter(":visible").each(function () {
$(this).triggerHandler("show");
});
visible.filter(":hidden").each(function () {
$(this).triggerHandler("hide");
});
return result;
}
});
Then when a child wants to listen for "show" or "hide" event I have to add him the class "displayObserver", and when It does not want to continue listen it, I remove him the class
bindDisplayEvent: function () {
$("#child1").addClass("displayObserver");
$("#child1").off("show", this.onParentShow);
$("#child1").on("show", this.onParentShow);
},
bindDisplayEvent: function () {
$("#child1").removeClass("displayObserver");
$("#child1").off("show", this.onParentShow);
},
I wish help
One way to do this.
Works only on visibility changes that are made by css class change, but can be extended to watch for attribute changes too.
var observer = new MutationObserver(function(mutations) {
var clone = $(mutations[0].target).clone();
clone.removeClass();
for(var i = 0; i < mutations.length; i++){
clone.addClass(mutations[i].oldValue);
}
$(document.body).append(clone);
var cloneVisibility = $(clone).is(":visible");
$(clone).remove();
if (cloneVisibility != $(mutations[0].target).is(":visible")){
var visibilityChangedEvent = document.createEvent('Event');
visibilityChangedEvent.initEvent('visibilityChanged', true, true);
mutations[0].target.dispatchEvent(visibilityChangedEvent);
}
});
var targets = $('.ui-collapsible-content');
$.each(targets, function(i,target){
target.addEventListener('visibilityChanged',VisbilityChanedEventHandler});
target.addEventListener('DOMNodeRemovedFromDocument',VisbilityChanedEventHandler });
observer.observe(target, { attributes: true, attributeFilter : ['class'], childList: false, attributeOldValue: true });
});
function VisbilityChanedEventHandler(e){console.log('Kaboom babe'); console.log(e.target); }
my solution:
; (function ($) {
$.each([ "toggle", "show", "hide" ], function( i, name ) {
var cssFn = $.fn[ name ];
$.fn[ name ] = function( speed, easing, callback ) {
if(speed == null || typeof speed === "boolean"){
var ret=cssFn.apply( this, arguments )
$.fn.triggerVisibleEvent.apply(this,arguments)
return ret
}else{
var that=this
var new_callback=function(){
callback.call(this)
$.fn.triggerVisibleEvent.apply(that,arguments)
}
var ret=this.animate( genFx( name, true ), speed, easing, new_callback )
return ret
}
};
});
$.fn.triggerVisibleEvent=function(){
this.each(function(){
if($(this).is(':visible')){
$(this).trigger('visible')
$(this).find('[data-trigger-visible-event]').triggerVisibleEvent()
}
})
}
})(jQuery);
example usage:
if(!$info_center.is(':visible')){
$info_center.attr('data-trigger-visible-event','true').one('visible',processMoreLessButton)
}else{
processMoreLessButton()
}
function processMoreLessButton(){
//some logic
}
$( window ).scroll(function(e,i) {
win_top = $( window ).scrollTop();
win_bottom = $( window ).height() + win_top;
//console.log( win_top,win_bottom );
$('.onvisible').each(function()
{
t = $(this).offset().top;
b = t + $(this).height();
if( t > win_top && b < win_bottom )
alert("do something");
});
});
$(function() {
$(document).click(function (){
if ($('#contentDiv').is(':visible')) {
alert("Visible");
} else {
alert("Hidden");
}
});
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="contentDiv">Test I'm here</div>
<button onclick="$('#contentDiv').toggle();">Toggle the div</button>
<div id="welcometo">Özhan</div>
<input type="button" name="ooo"
onclick="JavaScript:
if(document.all.welcometo.style.display=='none') {
document.all.welcometo.style.display='';
} else {
document.all.welcometo.style.display='none';
}">
This code auto control not required query visible or unvisible control