15 Efficient jQuery Tricks for Developers
1) Use the Latest Version of jQuery
With all the innovation taking place in the jQuery project, one of
the easiest ways to improve the performance of your web site is to
simply use the latest version of jQuery. Every release of the library
introduces optimizations and bug fixes, and most of the time upgrading
involves only changing a script tag.
You can even include jQuery directly from Google’s servers, which provide free CDN hosting for a number of JavaScript libraries.
<!-- Include a specific version of jQuery -->
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js"></script>
<!-- Include the latest version in the 1.6 branch -->
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6/jquery.min.js"></script>
The latter example will include the latest 1.6.x version automatically as it becomes available, but as pointed out on css-tricks, it is cached only for an hour, so you better not use it in production environments.
2) Keep Selectors Simple
Up until recently, retrieving DOM elements with jQuery was a finely
choreographed combination of parsing selector strings, JavaScript loops
and inbuilt APIs like
getElementById(), getElementsByTagName() and getElementsByClassName(). But now, all major browsers support querySelectorAll(), which understands CSS query selectors and brings a significant performance gain.
However, you should still try to optimize the way you retrieve
elements. Not to mention that a lot of users still use older browsers
that force jQuery into traversing the DOM tree, which is slow.
$('li[data-selected="true"] a') // Fancy, but slow
$('li.selected a') // Better
$('#elem') // Best
Selecting by id is the fastest. If you need to select by class name, prefix it with a tag –
$('li.selected'). These optimizations mainly affect older browsers and mobile devices.
Accessing the DOM will always be the slowest part of every JavaScript
application, so minimizing it is beneficial. One of the ways to do
this, is to cache the results that jQuery gives you. The variable you
choose will hold a jQuery object, which you can access later in your
script.
var buttons = $('#navigation a.button');
// Some prefer prefixing their jQuery variables with $:
var $buttons = $('#navigation a.button');
Another thing worth noting, is that jQuery gives you a large number of additional selectors for convenience, such as
:visible, :hidden, :animated and more, which are not valid CSS3 selectors. The result is that if you use them the library cannot utilize querySelectorAll(). To remedy the situation, you can first select the elements you want to work with, and later filter them, like this:$('a.button:animated'); // Does not use querySelectorAll()
$('a.button').filter(':animated'); // Uses it
The results of the above are the same, with the exception that the second example is faster.
3) jQuery Objects as Arrays
The result of running a selector is a jQuery object. However, the
library makes it appear as if you are working with an array by defining
index elements and a length.
// Selecting all the navigation buttons:
var buttons = $('#navigation a.button');
// We can loop though the collection:
for(var i=0;i<buttons.length;i++){
console.log(buttons[i]); // A DOM element, not a jQuery object
}
// We can even slice it:
var firstFour = buttons.slice(0,4);
If performance is what you are after, using a simple
for (or a while) loop instead of $.each(), can make your code several times faster.
Checking the length is also the only way to determine whether your collection contains any elements.
if(buttons){ // This is always true
// Do something
}
if(buttons.length){ // True only if buttons contains elements
// Do something
}4) The Selector Property
jQuery provides a property which contains the selector that was used to start the chain.
$('#container li:first-child').selector // #container li:first-child
$('#container li').filter(':first-child').selector // #container li.filter(:first-child)
Although the examples above target the same element, the selectors
are quite different. The second one is actually invalid – you can’t use
it as the basis of a new jQuery object. It only shows that the filter
method was used to narrow down the collection.
5) Create an Empty jQuery Object
Creating a new jQuery object can bring significant overhead.
Sometimes, you might need to create an empty object, and fill it in with
the add() method later.
var container = $([]);
container.add(another_element);
This is also the basis for the quickEach() method that you can use as a faster alternative to the default
each().6) Select a Random Element
As I mentioned above, jQuery adds its own selection filters. As with
everything else in the library, you can also create your own. To do this
simply add a new function to the
$.expr[':'] object. One awesome use case was presented by Waldek Mastykarz on his blog: creating a selector for retrieving a random element. You can see a slightly modified version of his code below:(function($){
var random = 0;
$.expr[':'].random = function(a, i, m, r) {
if (i == 0) {
random = Math.floor(Math.random() * r.length);
}
return i == random;
};
})(jQuery);
// This is how you use it:
$('li:random').addClass('glow'); 7) Use CSS Hooks
The CSS hooks API
was introduced to give developers the ability to get and set particular
CSS values. Using it, you can hide browser specific implementations and
expose a unified interface for accessing particular properties.
$.cssHooks['borderRadius'] = {
get: function(elem, computed, extra){
// Depending on the browser, read the value of
// -moz-border-radius, -webkit-border-radius or border-radius
},
set: function(elem, value){
// Set the appropriate CSS3 property
}
};
// Use it without worrying which property the browser actually understands:
$('#rect').css('borderRadius',5);
What is even better, is that people have already built a rich library of supported CSS hooks that you can use for free in your next project.
8) Use Custom Easing Functions
You have probably heard of the jQuery easing plugin
by now – it allows you to add effects to your animations. The only
shortcoming is that this is another JavaScript file your visitors have
to load. Luckily enough, you can simply copy the effect you need from
the plugin file, and add it to the
jQuery.easing object:$.easing.easeInOutQuad = function (x, t, b, c, d) {
if ((t/=d/2) < 1) return c/2*t*t + b;
return -c/2 * ((--t)*(t-2) - 1) + b;
};
// To use it:
$('#elem').animate({width:200},'slow','easeInOutQuad'); 9) The $.proxy()
One of the drawbacks to using callback functions in jQuery has always
been that when they are executed by a method of the library, the
context is set to a different element. For example, if you have this
markup:
<div id="panel" style="display:none">
<button>Close</button>
</div>
And you try to execute this code:
$('#panel').fadeIn(function(){
// this points to #panel
$('#panel button').click(function(){
// this points to the button
$(this).fadeOut();
});
});
You will run into a problem – the button will disappear, not the panel. With
$.proxy, you can write it like this:$('#panel').fadeIn(function(){
// Using $.proxy to bind this:
$('#panel button').click($.proxy(function(){
// this points to #panel
$(this).fadeOut();
},this));
});
Which will do what you expect. The
$.proxy function
takes two arguments – your original function, and a context. It returns a
new function in which the value of this is always fixed to the context.
You can read more about $.proxy in the docs.10) Determine the Weight of Your Page
A simple fact: the more content your page has, the more time it takes
your browser to render it. You can get a quick count of the number of
DOM elements on your page by running this in your console:
console.log( $('*').length );
The smaller the number, the faster the website is rendered. You can
optimize it by removing redundant markup and unnecessary wrapping
elements.11) Turn your Code into a jQuery Plugin
If you invest some time in writing a piece of jQuery code, consider
turning it into a plugin. This promotes code reuse, limits dependencies
and helps you organize your project’s code base. Most of the tutorials on Tutorialzine are organized as plugins, so that it is easy for people to simply drop them in their sites and use them.
Creating a jQuery plugin couldn’t be easier:
(function($){
$.fn.yourPluginName = function(){
// Your code goes here
return this;
};
})(jQuery);
Read a detailed tutorial on turning jQuery code into a plugin.
12) Set Global AJAX Defaults
When triggering AJAX requests in your application, you often need to
display some kind of indication that a request is in progress. This can
be done by displaying a loading animation, or using a dark overlay.
Managing this indicator in every single
$.get or $.post call can quickly become tedious.
The best solution is to set global AJAX defaults using one of jQuery’s methods.
// ajaxSetup is useful for setting general defaults:
$.ajaxSetup({
url : '/ajax/',
dataType : 'json'
});
$.ajaxStart(function(){
showIndicator();
disableButtons();
});
$.ajaxComplete(function(){
hideIndicator();
enableButtons();
});
/*
// Additional methods you can use:
$.ajaxStop();
$.ajaxError();
$.ajaxSuccess();
$.ajaxSend();
*/
Read the docs about jQuery’s AJAX functionality.
13) Use delay() for Animations
Chaining animation effects is a powerful tool in every jQuery
developer’s toolbox. One of the more overlooked features is that you can
introduce delays between animations.
// This is wrong:
$('#elem').animate({width:200},function(){
setTimeout(function(){
$('#elem').animate({marginTop:100});
},2000);
});
// Do it like this:
$('#elem').animate({width:200}).delay(2000).animate({marginTop:100});
To appreciate how much time jQuery’s
animation() save
us, just imagine if you had to manage everything yourself: you would
need to set timeouts, parse property values, keep track of the animation
progress, cancel when appropriate and update numerous variables on
every step.
Read the docs about jQuery animations.
14) Make Use of HTML5 Data Attributes
HTML5 data attributes are a simple means to embed data in a webpage.
It is useful for exchanging data between the server and the front end,
something that used to require outputting <script> blocks or
hidden markup.
With the recent updates to the jQuery
data() method, HTML5 data attributes are pulled automatically and are available as entries, as you can see from the example below:<div id="d1" data-role="page" data-last-value="43" data-hidden="true"
data-options='{"name":"John"}'>
</div>
To access the data attributes of this div, you would use code like the one below:
$("#d1").data("role"); // "page"
$("#d1").data("lastValue"); // 43
$("#d1").data("hidden"); // true;
$("#d1").data("options").name; // "John";
Read more about data() in the jQuery docs.
15) Local Storage and jQuery
Local storage is a dead simple API for storing information on the client side. Simply add your data as a property of the globallocalStorage object:localStorage.someData = "This is going to be saved across page refreshes and browser restarts";
The bad news is that it is not supported in older browsers. This is where you can use one of the many jQuery plugins that provide different fallbacks if
localStorage is not available, which makes client-side storage work almost everywhere.Here is an example using the $.jStorage jQuery plugin:
// Check if "key" exists in the storage
var value = $.jStorage.get("key");
if(!value){
// if not - load the data from the server
value = load_data_from_server();
// and save it
$.jStorage.set("key",value);
}
// Use value
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