Is binding events in jQuery very expensive, or very inexpensive? - javascript

I just wrote a $().bind('event') function and then got concerned that this kind of a call might be very expensive if jQuery has to run through each element in the DOM to bind this event.
Or maybe, it's just about as efficient as an event could be. The jQuery docs I've read aren't making this clear. Any opinions?

There are two things that can make your event binding code slow: the selector and the # of bindings. The most critical of the two is the # of bindings, but the selector could impact your initial performance.
As far as selectors go, just make sure you don't use pure class name selectors like .myclass. If you know that the class of myclass will always be in a <div> element, make your selector be div.myclass as it will help jQuery find the matching elements faster. Also, don't take advantange of jQuery letting you give it huge selector strings. Everything it can do with string selectors it can also do through functions, and this is intentional, as it is (marginally, admittedly) faster to do it this way as jQuery doesn't have to sit around to parse your string to figure out what you want. So instead of doing $('#myform input:eq(2)'); you might do $('input','#myform').eq(2);. By specifying a context, we are also not making jQuery look anywhere it doesn't have to, which is much faster. More on this here.
As far as the amount of bindings: if you have a relatively medium-sized amount of elements then you should be fine - anything up to 200, 300 potential element matches will perform fine in modern browsers. If you have more than this you might want to instead look into Event Delegation.
What is Event Delegation? Essentially, when you run code like this:
$('div.test').click(function() {
doSomething($(this));
});
jQuery is doing something like this behind the scenes (binding an event for each matched element):
$('div.test').each(function() {
this.addEventListener('click', function() {
doSomething(this);
}, false);
});
This can get inefficient if you have a large amount of elements. With event delegation, you can cut down the amount of bindings done down to one. But how? The event object has a target property that lets you know what element the event acted on. So you could then do something like this:
$(document).click(function(e) {
var $target = $(e.target);
if($target.is('div.test')) { // the element clicked on is a DIV
// with a class of test
doSomething($target);
}
});
Thankfully you don't actually have to code the above with jQuery. The live function, which is advertised as an easy way to bind events to elements that do not yet exist, is actually able to do this by using event delegation and checking at the time an action occurs if the target matches the selector you specify to it. This has the side effect, of course, of being very handy when speed is important.
The moral of the story? If you are concerned about the amount of bindings your script has just replace .bind with .live and make sure you have smart selectors.
Do note, however, that not all events are supported by .live. If you need something not supported by it, you can check out the livequery plugin, which is live on steroids.

Basically, you're not going to do any better.
All it is doing is calling attachEventListener() on each of your selected elements.
On parse time alone, this method is probably quicker than setting inlined event handlers on each element.
Generally, I would consider this to be a very inexpensive operation.

Related

Attaching event listeners using OnClick= or with script

Although it has already been asked, I want to adress the issue of correct jQuery programming.
Method #1:
<script>
function DoClickAction() {
// Some work
return false;
}
</script>
Do some work
VS
Method #2:
<script>
$(function() {
$("#ActionButton").on("click", DoClickAction);
}
function DoClickAction() {
// Some work
return false;
}
</script>
Do some work
I'm having a discussion with my colleagues about this, and my opinion is that both methods have enough pro and cons to not be able to say "this is the right way", but if I have to choose I tend to prefer Method #1, this is why:
Method #1 pros:
When debugging someone else code, you can easily follow which jQuery code is executed when somebody presses the link.
When you dynamically load (AJAX call) the content, it will always work, no need to rebind your jQuery events.
Method #2 pros:
It will produce less HTML code for the browser to download, because the script file will be cached and the onclick attribute is not necessary. Although this example uses more code.
You can re-use the code easily by using the same attributes, although using the onclick with 1 function is kind of the same thing.
What are your thoughts on this?
Instead of listing the pro's of either method, let me focus on the con's of method 1:
Change a function name == change the entire markup
All event handlers reside in the global scope. Working with closures can be a bit of a pain, then.
adding new elements dynamically (through JS or via ajax response) means that you'll either have to parse the markup and add the attribute one by one, or you'll have to send markup containing, essentially, JS function calls. Not safe, not clean
Each attribute is a new listener. The more attributes you have, the heavier the event loop will become
Mixing JS and HTML is not considered good practice. Think of it as separation of concern. The markup is there to provide the client with a UI. JS's job (in a browser) is to enhance the user experience. They have to work together, but have different tasks. Hence, they should be treated as separate entities.
As far as the second method goes, the only "cons" I can think of are:
Your code is slightly harder to understand, but if somebody can't work out what an event listener is, he shouldn't be working on your code, IMO.
Debugging can be harder, and older browsers might leak (jQ does contain an awful lot of X-browser related code, so it doesn't apply here. It does when you're writing vanillaJS)
In addition to this, method2 has another major pro, that you've not listed: delegation. At first, delegation looks hard, but It's easy, jQuery's $.delegate makes it easier, still, using $.on with a selector also delegates the event.
Basically, delegation allows you to deal with all events, for example click, for the entire page, or a section of the page, using a single listener. This as opposed to binding the event to each and every element. Thus: 1 listener on the event loop versus tens/hundreds. It's pretty obvious which is the more performant way of doing things.
Suppose you have a navigation div on a page, that looks like this:
<div id='nav'>
<ul>
<li id='nav-home'>Some pseudo-link</li>
<li id='nav-page1'>Another</li>
</ul>
</div>
You want to pick up on the user, clicking one of the <li> tags. The first method you listed makes for a right mess: <li id='nav-home' onclick='clickNav(event, this)'>. I'm passing the event object and this (a DOM reference) to have access to everything delegation gives me access to.
Using delegation, I can simply do this:
//jQ
$('#nav').on('click','li',function(e)
{
$.ajax({//you know the gist
url: 'ajax/' + $(this).id().replace('nav-',''),
success: function(){}
});
});
//vanillaJS:
document.getElementById('nav').addEventListener('click',function(e)
{
e = e || window.event;
var target = e.target || e.srcElement;
if (e.tagName.toLowerCase() === 'li')
{
//perform ajax call
}
},false);
I myself am very much partial to #2, as it provides a clean separation of JavaScript and HTML. The negatives of not having the action of a button be immediately visible in the HTML can be completely negated by browser plugins.
Furthermore, as you've already stated, sometimes I want to attach an onclick event to, say, every row of a table, and setting the OnClick attribute of an element on every row is much more wasteful than simply attaching a click handler to each of them with a single line of code elsewhere.

Handle stuff after dom changes

I've got a page with some Javascript / jQuery stuff, for example:
(function()
{
$('.tip').tooltip();
$('.test').click(function()
{
alert('Clicked!')
});
}();
On the page I insert some HTML with jQuery so the DOM changes. For example, I insert a extra element with the class "tip" or "test". The just new inserted elements doesn't work because jQuery is working with the non-manipulated DOM and the just inserted elements aren't there. So I've searched around and came to this solution for the "click":
$('body').on('click','.click',function()
{
alert('Clicked!')
});
I don't understand why, but this way it's working with the manipulated DOM and the jQuery stuff works on the new inserted elements. So my first question is, why does this work and just the click() function not? And the second question, why do I have to point to the "body"?
Finally, my third question is, how get this done with the tooltip?
I know that there is so many information about this subject (previous the delegate() and live() function I've read) but I can't found a explanation about it. And I can't get my third question solved with the information I found.
I'm looking forward to your responses!
Extra question:
4) Is it recommended to point always to the "body" for this kind of situations? It's always there but for possible performance issues?
So my first question is, why does this work and just the click()
function not?
Because the event handler is now delegated to a parent element, so it remains even after replacing/manipulating child elements.
Ancient article on event delegation for your perusal - but the concepts remain the same:
http://www.sitepoint.com/javascript-event-delegation-is-easier-than-you-think/
And the second question, why do I have to point to the "body"
You don't, any suitable parent element will do. For example, any direct parent (a div wrapper, for instance) which does not get replaced.
Finally, my third question is, how get this done with the tooltip?
You need to re-initialize your tooltip plugin on the newly inserted elements. For example:
$.get("foo.html", function (html) {
$("#someDiv").html(html);
$("#someDiv").find(".tip").tooltip();
});
The click() event doesn't work when you manipulate the DOM because JQuery is not watching for DOM changes. When you bind the click() event it is selecting the elements that are on the page at that time. New ones are not in the list unless you explicitly bind the event.
Because you have pointed the click() event on the body. JQuery then checks to see if the target of the click matches any of the event handlers (like what you have created) match the element clicked. This way any new elements will get the event 'associated' with them.
Because the tooltip isn't an event that you can place on the body, you will need to re-initialize it when the element is created.
EDIT:
For your fourth question, is it depends. The advantage of binding to the body is that you don't accidentally bind an event to an element more than once. The disadvantage is that you are adding event handlers that need to be checked on each event and this can lead to performance issues.
As for your concerns about DRY, put the initialization of the tooltips into a function and call that when you add them. Trying to avoid having the same function call is a little overkill in this regard, IMO.
Events are bound to the specific object you are binding it to.
So something like $('.tip').tooltip() will perform the tooltip() functionality on $('.tip') which is actually just a collection of objects that satisfies the css selector .tip. The thing you should take note of is, that collection is not dynamic, it is basically a "database" query of the current page, and returns a resultset of HTML DOM objects wrapped by jQuery.
Therefore calling tooptip() on that collection will only perform the tooltip functionality on the objects within that collection, anything that was not in that collection when tooltip is called will not have the tooltip functionality. So adding an element that satisfies the .tip selector, after the tooltip() call, will not give it the tooltip functionality.
Now, $('body').on('click','.click', func) is actually binding the click event to the body tag (which should always exist :P), but what happens is it captures whether the click event has passed through an element your target css selector (.click in this case), so since the check is done dynamically, new elements will be captured.
This is a relatively short summary of what's going on... I hope it helped
UPDATE:
Best way for your tooltip thing is to bind tooltip after you have added elements, e.g.
$('#container').load('www.example.com/stuff', function() {
$('.tip', $(this)).tooltip();
});

jQuery selector speed performation

I have a big table list of products, which is dynamic and changes with ajax. There is a for about 100 rows in that table.
I saw already that a contextual method $('.className', '#parentElement'); of selecting elements performs much better than usual $('.className'); or $('#parentElement .className');. (correct me if wrong)
In some circumstances i need to select a specific element with jQuery, there are dynamically added unique id="product-name-123456" and class="mainproductOffer" to each new row.
So, what performs faster from these two methods ?
$('tr[id^=product-name-]').click(function(){...});
$('tr.mainproductOffer').click(function(){...});
or
Is there any other method doing the same thing faster ?
In this case use the class selector, it is faster than the attribut selector.
You should use event delegation - for example:
$('table').on('click','.mainproductOffer',function() {});
to reduce the number of event handlers. If the class (mainproductOffer) is only used for the TR tag, remove the Tag from the selector too.
So, what performs faster from these two methods ?
$('tr.mainproductOffer').click(function(){...});
Is there any other method doing the same thing faster ?
Unsurpassed article 'jQuery Anti-Patterns for Performance' would help you
Use on() (event delegation), since its dynamically added.
Class selector is faster than attribute selector
$('tr').on( 'click', '.mainproductOffer', function(){...});
$('tr.mainproductOffer').click(function(){.....; OR
$('table').on( 'click', 'tr.mainproductOffer', function(){...;
are faster since
according to the jquery documentation
jQuery can process simple selectors of the form tag#id.class very quickly when they are used to filter delegated events. So, "#myForm", "a.external", and "button" are all fast selectors. Delegated events that use more complex selectors, particularly hierarchical ones, can be several times slower--although they are still fast enough for most applications. Hierarchical selectors can often be avoided simply by attaching the handler to a more appropriate point in the document. For example, instead of $("body").on("click", "#commentForm .addNew", addComment) use $("#commentForm").on("click", ".addNew", addComment).

Optimising Jquery code - Adding and removing classes on click

I am currently learning js and jquery to assist me with my designs, a common problem that I am having is that I can get it to do what I want it to but I have no idea if the way in which it has been coded is efficient. Could anyone see a better way to code this:
$(".cal-check a").click(function(e) {
e.preventDefault();
$(".agenda").addClass("active");
});
$(".agenda .close-panel").click(function(e) {
e.preventDefault();
$(".agenda").removeClass("active");
});
I want to click on a calendar event then it adds the class active to another class within the calendar called agenda which then brings up the agenda. I then remove it by clicking on a close panel element. Many thanks
You could cache the .agenda selector like so:
var $agenda = $(".agenda");
$(".cal-check a").click(function(e) {
e.preventDefault();
$agenda.addClass("active");
});
$agenda.find(".close-panel").click(function(e) {
e.preventDefault();
$agenda.removeClass("active");
});​
I recommend not changing classes, that will usually be rather intensive on the browser, because one class change will mean that all the classes have to be reparsed. This is usually very bad for more aggressive stuff, like animation, but if you have performance considerations, you should take that into advisement.
I think this is already efficient.
Just something that might help in the future is to try and dive into the DOM as little as possible. In this small example it wont make a difference but for example create a variable for agendaClass instead of using jquery every time to fetch it.
var agendaClass = $(".agenda");
$(".cal-check a").click(function(e) {
e.preventDefault();
agendaClass .addClass("active");
});
$(".agenda .close-panel").click(function(e) {
e.preventDefault();
agendaClass .removeClass("active");
});
That should be efficient enough. How you can optimize your code strongly depends on your DOM structure.
Behind the scene, jQuery with its Sizzle search engine will use built in methods for DOM search, if those are available (native search will be always faster than search done with JS). In your case everything should be Ok, especially in modern browsers, as they have querySelectorAll and .cal-check a and .agenda selectors will be executed with that built in method. Also, there is getElementByClassName which could be used to find .agenda.
Both of those methods are supported by most of modern browsers (provided links have a list of supported browser), so talking about browsers like IE8+, Firefox and Chrome will be fast enough with your selectors. At the same time IE7 has no functions like above and Sizzle will be forced to go through numerouse elements to find elements you are looking for. Maybe you can limit that amount specifying some container with id, in that case it will look inside that elements only:
$("#someId .agenda"), for instance. You may want additionally add some tag: $("#someId div.agenda"). This way you will limit amount of elements to search with divs (getElementsByTagName could be used) inside #someId (getElementById). That way you may increase speed in IE7 and other old browsers with no support of getElementByClassName and querySelector
Plus, you may cache search results as it was already mentioned here.

jQuery Live traversal parent() selector

$(".hovertip").parent().live('hover', function() {
...
The above code doesn't seem to register.
This doesn't seem to work either:
$(".hovertip").parent().live({
mouseenter:
function() {
...
Any examples of .live, .delegate, .bind, or .on working with a jQuery selector and a .parent() selector with .hover() or mouseenter: and mouseleave:?
Update: I've created a separate question to address the dynamic DOM issue this Question has raised: jQuery .on() with a .parent() and dynamic selector
Try:
$(".hovertip").parent().on('hover', function() {
alert('yay');
});
Note: .on was introduced in jQuery 1.8.
Working demo http://jsfiddle.net/pRB8n/ Hover over test test - in the demo
If you really want to use .delegate try this please: http://jsfiddle.net/TURBX/2/ - http://api.jquery.com/delegate/
Delegate
Attach a handler to one or more events for all elements that match the
selector, now or in the future, based on a specific set of root
elements.
Hope rest fits the needs :)
P.S. - .live is deprecated: for further if you keen - my old post here: :) What's wrong with the jQuery live method?
under category you will see: http://api.jquery.com/live/ "deprecated"
I would add a comment to Tats_innit's post, but I can't.
As per the documentation on live,
Chaining methods is not supported. For example, $("a").find(".offsite, .external").live( ... ); is not valid and does not work as expected.
That's why .parent() does not work.
Binding to parent
Event delegation (handled by the deprecated live and .delegate, and now by .on/.one) only moves downwards. You can't have an upward event delegation like you seem to want to do here.
That is to say if the parent of ".hovertip" does not exist then clearly ".hovertip" does not exist so you are actually binding to nothing.
If your goal is to bind the event to the parent of ".hovertip" when it appears, then you're SOL since delegation only moves downwards (to descendants).
Your options to handle that would be:
* Bind to the parent of .hovertip when it is appended to the DOM.
* Know a selector for the parent of .hovertip ahead of time and bind to it immediately, perhaps through delegation.
Delegating to child
If your goal is to have the event fire when .hovertip is hovered, but .hovertip may not be in the DOM and its parent is not known, you must use a method like this:
$("known parent selector of .hovertip").on('hover', '.hovertip', function () {
"known parent selector of .hovertip" has to be an element that you know ahead of time. If you can't know, you have to use document, but I'd suggest to try to get as close as possible. You can only use this on elements that exist in the DOM at the time of binding.
I think what you are looking for, actually, is something along these lines:
$(document).on('mouseover', '.hovertip', function() {
// handle your mouseover changes, here
});
$(document).on('mouseout', '.hovertip', function() {
// handle your mouseout changes, here
});
.live, .bind, are all deprecated, AFAIK, which means they'll go away in the future, and you might not want to rely on their continued support.
It would also be far better to replace $(document) with a selector that's closer to your .hovertip elements, but above them in the DOM nesting, so they can respond to your event, but without forcing jQuery to watch for every event on every element in the whole document. I simply put document in there as an example, as I don't know what the rest of your structure looks like.
http://jsfiddle.net/mori57/qa7py/
As I think about it, I think it's worth pointing out that throwing things to .parent() may not always work out the way you expect, especially if you're modifying the DOM. I think it's far safer to set a higher-level event handler.
If you must use something like the .parent(), I always found more accurate results with .closest(), and giving it a selector also helps the parsing engine narrow its search. You don't want one parent triggering the hover state for /all/ the .hovertips at one time, which could happen in some cases.

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