Fortunately, jQuery makes it super easy to differentiate the Ajax requests from normal page views.

X-Requested-With Header

If you were to browse the jQuery source, you would see that jQuery adds a special HTTP header to (almost) every Ajax request it makes with $.ajax(), $.get(), $.getJSON(), $.post() and .load() methods.

Keep in mind, though, that the header is not sent with $.getScript() or any JSONP request made with $.ajax() or $.getJSON(), since they aren't technically Ajax requests.

Detection on the Server

By checking for this header, you can easily determine on the server if the request was initiated by jQuery. Each server-side language and web server combination will give you different ways of accessing this header, but let's look at a few.

In PHP, you can use this function to determine the type of request:

Sinatra and Ruby on Rails have special shortcuts already built in:

Since other libraries outside of jQuery also set the X-Requested-With header, many server languages have special support for reading it. Check the documentation for your favorite server language to see if it has any convenience methods for detecting an Ajax request.

A Small Example

Ok, let's apply this knowledge to add Ajax to a simple email signup form. Here is our existing HTML:

And here is the existing email.php (Note: on a normal error you might redirect back to show a message, or render the form again. This is for example only):

The previous two pages work together to provide a simple signup functionality, without JS or Ajax involvement.

Now let's add the Ajax. We’ll add the following to the form page:

Finally, we replace the initial PHP code block in our email.php file to take advantage of the Ajax submission:

Conclusion

That's it! A few lines of code, and your server side code can now render different content depending on how the request was generated. Now that you know how to detect jQuery Ajax events, you no longer need to resort to passing ajax: true as data on your requests or calling a separate file altogether.

Then appended some photos via ajax later on:

The click event would still apply to that new image without having to re-bind the event. Handy, isn't it?

Not too long ago, the .live() method was brought up for discussion for a few reasons. One problem discussed is that .live() fails when you try to use it alongside traversals like:

and also when you pass any native DOM elements like:

Unfortunately, when you use .live(), it has to be at the top of the chain like so:

Because this can be frustrating and confusing for many users who are used to the traversing and chainability that jQuery offers, it sparked a discussion about the syntax for .live(). Why does it look like all the other methods, yet does not behave the same? Since changing the syntax would result in a whirlwind of code breakage, the jQuery team decided to introduce .delegate() and .undelegate() to complement .live() and .die(). Here's an example of how you would normally use .live() and .die() and how you can now use .delegate() and .undelegate():

Old way

New way

The benefit of delegate() is that it allows you to specify its context. This way, it ensures that we do not bubble all the way up the DOM tree to capture the target of the element. With the .live() method, it bubbles all the way up the DOM each time unless you set context like so: $('td', $('table')[0]).live('hover', function(){}). That just looks ugly.

Some often like to think of delegate() like a bind() call. The syntax is a little different as you can see below.

In short, the difference between .bind() and .delegate() is that .bind() will only add events to the elements that are on the page when you call it. .delegate() is listening for new elements and then adding events to them when they appear on the page.

The gotchas of delegate

While it does behave like .bind(), it does not allow you to pass an object map of events like .bind() does. Take this .bind() method for example:

An error will be thrown when you try to do:

I'm not sure the reasoning behind not implementing this, but I guess I'm not the only one pondering it.

Granted, .bind() didn't have this feature until jQuery 1.4. But if you'd like this same feature in .live() and .delegate(), Robert Katic wrote a small piece of code that you can include. Grab the gist here.

I recommend using Robert Katic's patch above, but of course there are other approaches people can take. For example, you can rig up your own custom object map:

Another "gotcha" with both .delegate() and .live() is that when you add the events mouseenter and mouseleave to an element, and then check the event type (e.type) in the callback function, it incorrectly displays as mouseover and mouseout. Using .bind(), on the other hand, it displays as mouseenter and mouseleave as expected. Here is an example:

UPDATE: This has been fixed and will be rolled out in the next version of jQuery.

Overall, the "gothcas" are no match for the benefits that .delegate() and .undelegate() provide. Truly great additions to the jQuery core.

From traditional event listening to event delegation

Since an event occurring on an element is propagated to all of its ancestors, an event listener can be bound to a single ancestor of numerous elements instead of being bound to all the elements individually.

Consider the following list items:

If we want to display the class of an item when it is clicked, a traditional event listener in jQuery would be written like this:

The event object passed to the handler has a target property which corresponds to the element that has been clicked.

The equivalent using event delegation would look like this:

Event delegation has two main advantages:

1. setting a single event listener instead of multiple ones is obviously faster;
2. any new element later added to the list will have the same behavior (as demonstrated in Working with Events, Part 1).

This translation to event delegation that we've just made is, however, slightly too simple, since our original aim was to display only the class of the list items. Using the previous snippet, the class of the unordered list itself can be displayed (by clicking to the left of a bullet-point). We thus have to make sure that the target of the click is a <li>.

Scanning the ancestors of the event.target: the .closest() method

With such a simple document, event delegation is really that easy to achieve. But things can get more complex if the items have children elements:

In this case, if the user clicks on one of the words item, the event.target will be a <u>. It is therefore necessary to loop through all of the ancestors of this original target to find the element that is "interesting" for us: the <li>

Notice that if the user clicks outside of an <li>, we have to stop looping through the ancestors at some point; in this case when we find the root of the document (which has no parentNode).

jQuery 1.3 introduced the .closest() method, which replaces this loop by a single line of code:

The parameter passed to the .closest() method is a CSS selector that will match the first interesting ancestor.

The context parameter

It can be noted that, when the click occurs outside of an <li>, we could stop looping through the ancestors before hitting the document root, but instead as soon as we hit the <ul>. jQuery 1.4 will introduce an optional context parameter to .closest() for this purpose:

Here this is the <ul> element to which the event listener has been bound. This optional parameter improves the performance of event delegation as it prevents the wasted resources of searching for an ancestor which cannot exist.

Event delegation in a single line: the .live() method

jQuery 1.3 also introduces .live(), a method which binds the event listener and implicitly calls the .closest() method to determine whether your event handler should be executed or not.

Note how different the syntax using the .live() method is. It seems that we have switched back to a traditional event binding. However, a big difference is that the event listener will work for any existing and future element matching our original selector. There is, of course, nothing magic: behind the scenes .live() simply binds the event listener to the document root and filters any event.target using the .closest() method.

A notable difference with the traditional event binding syntax is that we are not using the target property of the event object inside our event handler, but rather the currentTarget. Indeed, the target of the event is possibly a child of one <li>, whereas the currentTarget property refers to the element that has been found by the implicit .closest().

As explained on the Event Object documentation, the currentTarget property is supposed to be the current DOM element within the event bubbling phase, i.e. the element on which the event has been detected by the event listener, which will always be the element on which the event listener was bound. When using .live(), the currentTarget would therefore always be the document root and you would need to use .closest() once again on the original target to find an interesting ancestor.

This kind of code is required with jQuery 1.3, but as of jQuery 1.4, the currentTarget is modified internally and can thus be used to avoid the extra .closest() inside the event handler.

The context parameter

In jQuery 1.3 all live event listeners were effectively bound to the document root. This can hurt the performance of a web page since all events detected by an event listener will trigger the execution of an implicit .closest(), even though the event target might be totally out of interest.

In jQuery 1.4, .live() should be able to bind the event listener to a specific and more focused element of the document by taking advantage of the context of your jQuery object:

The context is the second parameter used to build our jQuery object. To be useful for .live() it has to be set as a pure DOM element, hence the [0] after $("ul"). Brandon Aaron has a useful article explaining the context parameter in detail.

Unbind for .live(): the .die() method

Just like .bind() has its .unbind() counterpart that allows for event listeners to be unbound, .live() has its .die() counterpart.

Unlike .bind(), .live() does not allow for namespaced events to be used.

Dealing with events that don't bubble

There are some events for which event delegation is traditionally not possible, simply because they do not bubble. The promise of jQuery 1.4 is nevertheless to make those events compatible with .live(). How this is achieved will be covered in the upcoming fourth part of this tutorial.

The Styles

For the navigation items, I used a simple unordered list wrapped in a <div class="nav">. While the HTML structure is straightforward, the CSS is a little tricky, so I'll detail it here:

Most of the relevant CSS here has to do with positioning the nav items. I set the top <ul>'s left margin to 75 pixels less than the wrapper's width so that the top-level links appear on the right side. The 1600px width for the <ul> gives the floated list items ample room to line up horizontally next to each other.

The wrapper's overflow declaration is significant, as it hides the list items when they're sticking out to the right, but the rest is "window dressing."

Sliding the Nav

With the nav looking the way I want it at its initial state, it's time to make it do something. I'll start with a simple setup, having each "tab" (top-level item) slide to the left on the first click to reveal its sub-nav items, and slide back to its initial position when it's clicked a second time.

For this basic behavior, everything can be done inside a click handler for the top-level links. Note: Since I'm using multiple navs for this tutorial, each with its own set of behavior, I'll be referring to them by ID, unlike in the CSS snippet above, where everything is styled by class. There is nothing special about the selectors or their naming here. Name your own elements and select them however you want.

The first thing to do is set a few variables. The $parentItem variable is the <li> parent of the clicked link. The slideAmt is the width of the nested <ul>, which is the next sibling of the link. And direction will eventually determine whether the parent <li> should be slid to the left or to the right.

Notice the use of $(this). Inside the click handler, this refers to the clicked DOM element. By wrapping this in $(), we can call jQuery methods on it.

To get the sliding motion to occur, we can animate either the left property or the marginLeft property. Here, I'll animate marginLeft. So, the next thing to do is determine the direction of the animation based on the current value of marginLeft: If it's less than 0, direction is set to "+=", which increases it (back to 0); otherwise, direction is set to "-=". At the same time, an "expanded" class will be toggled so that the arrow background image can change directions.

Finally, we do the animation, plugging in the direction and slideAmt variables. The return false; line stops the default click action from occurring. Here is the finished code for the basic implementation:

Give it a try:

One at a Time

That's all well and good, but I don't really care for having more than one row of items expanded at a time. A couple simple modifications will fix that for us:

The links are stored in a variable first thing here. Whenever a link is clicked, all links have the "expanded" class removed. Of course, only one, at most, will have that class, but I'm lazy and it's easier to tell all of the links to remove the class than it is to hunt links that have the class first.

The same check is performed to set the direction of the animation. If the clicked link's parent <li> is going to be slid to the left, the link will also get the "expanded" class.

Finally, the clicked link's parent is animated in the direction and number of pixels specified by the variables. But here's the twist: all of that parent's siblings have their marginLeft property animated to 0. Again, I'm taking the lazy route, animating all of the siblings, even though one or none of them will need it.

Here's a demo of the "one at a time" version:

Auto-Collapse

Now that the expanding and collapsing are happening the way I like it, I'll add one more little touch. If the user's mouse leaves the containing <div class="tab-nav">, and stays out for a full second, any expanded list will collapse.

Line 2 declares a variable that will be used for the setTimeout(), which you can see tucked inside the .mouseleave() method near the bottom of the code. The setTimeout() function has two arguments: the first is an anonymous function that contains code for triggering the collapse of the list items, and the second is the number of milliseconds to wait (1,000 milliseconds) before the first argument (the anonymous function) is executed. The clearTimeout() inside the .mouseenter() method does what its name suggests: it clears the timeout. If the user mouses out of the nav area but then mouses back in before the 1000 milliseconds are up, the timer is stopped and the function will not be executed.

Note: The mouseenter(fn) and mouseleave(fn) shorthand methods are available as of jQuery 1.3. If you're still using jQuery 1.2.6, you can use .bind('mouseenter', fn) and .bind('mouseleave', fn) instead. Or, with just about any version of jQuery, you can use .hover(fn, fn).

Here is the final demo:

There are many ways to do this sort of thing. Just tweak the CSS or change the animation for a completely different experience.

Setting up Your Files for jQuery IntelliSense

First, set up jQuery on your page by downloading the latest version from the jQuery site.

Next, you will need to download the jQuery Documentation file from the jQuery site.

Download the files and add them to your project.

IntelliSense in external JavaScript files

At the top of the JavaScript file in which you would like to have jQuery IntelliSense enabled, you will need to add a line to reference the documentation file:

/// <reference path="jquery-1.3.2-vsdoc2.js" />

IntelliSense inline on your ASPX page

There are a couple of scenarios that may affect if you include a reference to the VSDOC file or not. If in doubt, just add a reference to the documentation file.

If you are linking to jQuery by the Google Code AJAX Library or are linking to jQuery from anywhere outside of your project you will need to reference the documentation file.

From each ASPX page you want jQuery IntelliSense you’ll want to call the reference within a server-side conditional statement so that the documentation file will still load in Visual Studio but will not load at run-time. Add the following after your jQuery declaration:

If you downloaded jQuery and saved it to your project Visual Studio will look for the vsdoc.js file automatically if the following conditions are met.

You've downloaded and installed the hotfix for Visual Studio.

jQuery and the documentation file need to be named the same with the exception that the documentation file end with -vsdoc.js. So when you add jQuery to your project make sure to rename them similarly. For instance, jquery-1.3.2.js is your jQuery library, Visual Studio will look for the documentation file at jquery-1.3.2-vsdoc.js and load it.

(Note: the jQuery 1.3.2 documentation file is named jquery-1.3.2-vsdoc2.js on the Download page so make sure you take out the 2 so that the file will be found by Visual Studio)

If you can't meet these conditions you'll need to reference the documentation file as shown above.

To test to make sure the documentation file loaded correctly, you can type $( and you should be presented with some documentation.

Additionally, you can type in $(document).r and you will be presented with a drop down of available options to choose from, one being "ready."

Now as you write your jQuery code, you'll be helped along by seeing what methods and properties are available to you.

Related Links

• Rich IntelliSense for jQuery
• jQuery and Microsoft
• jQuery, Microsoft and Nokia
• VS2008 SP1 Hotfix to Support "-vsdoc.js" IntelliSense Doc Files

1. I can't change jQuery's API.
2. Those shorthand methods used to be part of jQuery core, but with the release of 1.0, John Resig cleaned up the API quite a bit, removing all of the .unEvent() and .oneEvent() methods.

While I understand the desire for simplicity in developers' code and consistency in jQuery's API, I think Mr. Resig made the right decision removing the shorthand methods. Keeping both "un" and "one" shorthands in there would have meant an additional 44 methods, with very little gain for most users of the library. Nevertheless, it's fairly trivial to create a plugin for this sort of thing.

If we want the shorthand methods for a particular project, we can simply iterate through an array of event types and add the "un" or "one" method to the jQuery prototype (jQuery.fn). Here is what it might look like:

To add the "one" shorthand methods, we can repeat lines 8– 9, using one in place of both un in line 8 and unbind in line 9.

The script will respond to mouseover, mouseout, and click within <div class="entrytext">. I use mouseover/mouseout rather than mouseenter/mouseleave because the script relies on event bubbling. The $(event.target) selector ensures that the class manipulation occurs on the innermost element. You can try it out on this page by hovering over elements within the main content area.

The two classes that are being toggled have the following style rules:

The outline property is really handy for this sort of thing because it doesn't affect the element's dimensions or layout. Unfortunately, it isn't supported in Internet Explorer 6 or 7, so if you want to support them, you might want to use border or background-color instead in a separate IE-only stylesheet. Or, maybe IE has some proprietary property? Anyone know?

I'm not sure what the person wanted to do with this script. By itself, it doesn't seem particularly useful to me. Still, I think there are a few concepts in there that can be applied elsewhere, and maybe the script can be expanded to do something interesting.

Notice that the updated script also takes advantage of the .closest() method, which was introduced in jQuery 1.3. I don't want to apply the outline to any of the syntax-highlighted code in the entry, so I make sure that neither the event target nor any of its ancestors has a class of "syntax_hilite." Remember, to test for the presence (or absence) of a selector, we need to include more than just the selector itself. Here I test for "not a length." What I'm actually looking for is a length of 0, but since 0 is "falsey" the ! operator works just fine here.

One More Tip

Come to think of it, I can make the script shorter still by including the click event type along with mouseover and mouseout. Then, inside the the handler, the class that is toggled is determined by event.type.

Sometimes when code becomes shorter, it can also get less readable and more difficult to modify later on. I'm not suggesting that the final code snippet is necessarily the best way to achieve the outcome. A lot depends on what else you're planning to do and how a certain piece fits into the project as a whole.

The Bookmarklet

To use the bookmarklet, drag the following link to your bookmark/favorites list:

» [inline]jQuerify[/inline] «

Then, when you're on a page in which you want to play around with jQuery in the console, just click the bookmarklet.

Problems with the Other One

The biggest problem with the former version was that it didn't work when other libraries that use the $ function, such as Prototype and Mootools, were already loaded on the page. A number of people in the comments suggested that I simply add a jQuery.noConflict(); line to the script. But I wasn't crazy about the idea of having to use jQuery() instead of $() even if no other libraries had been loaded.

Another problem, one that I noticed while testing my new version, was that sometimes the jQuery file that I was inserting from the Google CDN wouldn't fully load by the time I attempted to use it later in the bookmarklet. At least, I think that's what was going on. In any case, it was throwing a "jQuery is not defined" error.

A Few Improvements in This One

To handle the problems, I'm having the script do a few things differently:

• Set up a counter to check 10 times if jQuery is loaded before giving up.
• Use a setTimeout to put a one-quarter-second (250ms) delay interval in between attempts.
• Check if the $() function is already being used by another library. If it is:
  • use jQuery's $.noConflict function to release the $() to the other library.
  • set $jq as an alias to jQuery for convenience.
  • mention in the flash notice that jQuery is in noConflict mode and that $jq() should be used instead of $().
• If after multiple attempts jQuery still won't load for some reason, set the flash notice's message accordingly and then remove it through plain old JavaScript rather than jQuery.

Here is the script in its unbookmarkleted form:

I'm sure it can be improved even further. If you have suggestions for making it more elegant, more efficient, more betterer, I would love to hear them in the comments.

Let me know if this one causes any problems.

1. Update Attribute Selectors

By far the most common stumbling block to the 1.3 upgrade has been the attribute selector. The XPath syntax for this selector — [@attribute] — has been deprecated since version 1.1.4 in August, 2007. Still, many scripts, including some prominent plugins, continued to use the old syntax, which wasn't a problem until jQuery 1.3, at which point it was no longer supported. The correct syntax (since 1.1.4) follows the CSS standard: [attribute].

The fix is quite simple. Simply search your scripts for [@. Go through the matches one by one, and if the string is being used as an attribute selector (and not, for example, in a regular expression), replace it with [.

Removed XPath Syntax

This will break your code in jQuery 1.3+:

Current CSS Syntax

Use this instead:

2. Check Custom Selectors

If you are using custom selectors, either in your own script or within a plugin, you might run across an error if the second argument's object value is a string:

This is another easy fix. Simply change that value to an anonymous function and add what was in the string to the return statement:

So, basically, you just change "jQuery(a).siblings(m[3]).length>0" to function(a,i,m) {return jQuery(a).siblings(m[3]).length>0;}.

When someone on the jQuery Google Group was having trouble with George Adamson's excellent More Selectors plugin, all I had to do to make it compatible with jQuery 1.3 was update the attribute selectors and change custom selectors (my updated script is available here temporarily until George has time to update the original).

3. Note Visible and Hidden Elements

This change didn't occur until jQuery 1.3.2, but if you are upgrading to the latest and greatest jQuery version, you'll want to be sure your scripts aren't relying on a quirk in how jQuery was determining the visibility of elements. Prior to 1.3.2, if you had an element with display:block inside a containing element with display: none, the inner element would still be reported as visible.

Before version 1.3.2, $('#inner'1).is(':visible') would return true and $('#inner1:hidden') would match 0 elements. In order to find out if an element were truly hidden, meaning you couldn't see it, you'd have to check all of its ancestors to see if they were hidden as well. Remy Sharp put together a little custom selector to check if elements were *really* visible.

With 1.3.2, $('#inner').is(':visible) returns false and $('#inner:hidden') match 1 element.

Another Visible Wrinkle

There is one more change in how visibility is detected in 1.3.2: elements with visibility: hidden are now considered visible, whereas before they were considered hidden.

Given the above div structure, jQuery 1.3.2 considers #inner2 visible while prior versions considered it hidden.

Here is a quick demo, with two iFrames showing the differences in determining visibility:

I'm not sure how I feel about the new behavior with visibility:hidden, but I think the change was important for performance reasons.

A Few Others

There are a few other issues that may affect a small minority of users, but the three above represent the lion's share of reported problems that I've seen on the Google Groups. For more information about changes, see the jQuery 1.3 Release Notes

Reverse the Slide Direction

With the built-in slide methods, elements are shown by sliding them down and into view. But what if we want to slide something from the bottom up and into view? The trick here is to use some judicious CSS. Let's start with a simple HTML structure:

To get the inner div to slide up, we'll anchor its bottom edge to the bottom of the bottom of the nearest positioned ancestor (in this case, the #slidebottom div):

Other properties such as width, padding, margin, and background-color have been set for these elements, but only the essential properties for modifying the slide behavior are shown above.

Note: I'll be using the term positioned to refer to elements that have the CSS position property set to something other than "static." Both divs in this example are positioned — one absolutely and the other relatively.

Now, we can write the jQuery the same way we would with a traditional slide effect:

Try it out:

Horizontal Slides

Animate Width

We can also slide elements to the left and right. The simplest way is to animate the element's width property.

In this case it's not necessary for the sliding element to be positioned.

While animating the width is fine for what it is, I'm not crazy about how the text wraps as the width decreases. One way to avoid the wrapping is to add a CSS declaration such as white-space: nowrap;, but that would mess up the appearance of an element with a lot of text—one in which we would expect to see text wrapping when it is at full length.

Animate Left

Another way to avoid the text-wrap issue is to animate the element's left property. Here, it's important once again to make sure that the element is positioned. After all, we can't move an element if it's static.

With this animation, we need to calculate how far to move the element. The following code rests on two assumptions: (1) the sliding element has an outerWidth() that is equal to or greater than its parent element's width, and (2) the sliding element is initially set to left: 0;. You may have to adjust your code if either one of these assumptions doesn't hold in your situation.

Lines 5 through 7 use a "ternary" operator that basically says, "If the left css property equals 0, move the element to the left as many pixels as it is wide (including padding and border); if not, move it back to 0."

Also, if we want the element to be hidden when it slides to the left, we need to add overflow: hidden; to its parent element.

Animate Left Margin

Finally, we can achieve the same effect as the left animation by animating the marginLeft property. In this case, we still need overflow: hidden; on the parent element, but the sliding element does not need to be positioned.

For the sake of variety, we're sliding this one to the right.

With a couple little tweaks, these horizontal slides can be used for a horizontal accordion.

Further Resources

• To learn about adding easing effects to your slides, check out Brandon Aaron's Quick Tip: Add Easing to Your Animations.
• To convert any of these slides into a plugin for convenient reuse, see Simple Effects Plugins.
• For a whole bunch of ready-made slides and other effects, take a look at jQuery UI.