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jQuery Essential Training

Using global AJAX event handlers


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jQuery Essential Training

with Joe Marini

Video: Using global AJAX event handlers

The jQuery AJAX library provides a set of global AJAX event handlers that you can use to register functions to listen in for interesting events that take place during the lifecycle of an AJAX request on a given page. Here in the API documentation let's go ahead and click on the global AJAX event handlers, and you can see that there is about a half dozen functions that you can use to register events for when something interesting happens in an AJAX request. Now again, these are not functions that you call; these are functions that get called for you.
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  1. 2m 52s
    1. Welcome
      1m 9s
    2. Using the exercise files
      1m 43s
  2. 17m 37s
    1. What is jQuery?
      5m 19s
    2. Downloading and installing jQuery
      2m 20s
    3. Creating a simple jQuery-enabled page
      7m 12s
    4. Overview of jQuery's features
      2m 46s
  3. 59m 57s
    1. Overview of selectors and filters
      2m 9s
    2. Using basic jQuery selectors
      9m 6s
    3. Using basic jQuery filters
      8m 35s
    4. Using jQuery attribute filters
      6m 7s
    5. Child, visibility, and content filters
      9m 59s
    6. Form selectors and filters
      9m 3s
    7. Traversing documents
      9m 1s
    8. Understanding jQuery statement chaining
      1m 42s
    9. Practical example 1: Annotating page links
      4m 15s
  4. 47m 16s
    1. Creating, getting, and setting content
      5m 53s
    2. Manipulating attributes
      5m 43s
    3. Inserting content
      4m 57s
    4. Wrapping, replacing, and removing content
      5m 27s
    5. Working with CSS
      6m 19s
    6. Associating data with page elements
      9m 30s
    7. Practical example 2: Automatic TOC generator
      9m 27s
  5. 33m 6s
    1. Understanding the jQuery event handling features
      2m 4s
    2. Binding and unbinding events
      6m 23s
    3. Convenient event helper methods
      4m 40s
    4. Using the jQuery event object
      6m 21s
    5. Using miscellaneous event features
      4m 38s
    6. Practical example 3: Table striping and highlighting
      9m 0s
  6. 28m 45s
    1. Hiding and showing elements
      5m 23s
    2. Fading elements in and out
      4m 2s
    3. Sliding elements
      4m 3s
    4. Creating custom animations
      5m 58s
    5. Practical example 4: Image rotator
      9m 19s
  7. 25m 30s
    1. Introduction to jQuery UI
      3m 40s
    2. Exploring the jQuery UI widgets
      5m 24s
    3. Exploring the jQuery UI effects
      3m 58s
    4. Using the jQuery UI ThemeRoller
      4m 11s
    5. Downloading and installing jQuery UI
      8m 17s
  8. 47m 49s
    1. Overview of the sample web site
      3m 50s
    2. Using the accordion widget
      9m 14s
    3. Creating an image rotator
      10m 22s
    4. Building hover tooltips
      7m 26s
    5. Making an image selector
      9m 30s
    6. Using the Resizable effect
      7m 27s
  9. 30m 2s
    1. Working with Asynchronous JavaScript and XML (AJAX)
      10m 8s
    2. Using AJAX helpers
      4m 34s
    3. Understanding AJAX data types
      10m 14s
    4. Using global AJAX event handlers
      5m 6s
  10. 20s
    1. Goodbye
      20s

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jQuery Essential Training
4h 53m Beginner Sep 01, 2009 Updated May 24, 2013

Viewers: in countries Watching now:

In jQuery Essential Training, Microsoft professional Joe Marini presents the power of the jQuery library, an open-source JavaScript project that greatly simplifies the process of adding advanced functionality to web sites. Joe teaches how to use these new features to build pages that work across browsers with the functionality that today's users (and clients) are looking for, from complex animation effects to dynamic page formatting. Joe pulls all of this together, showing how the jQuery UI plug-in can expand and streamline the capability of jQuery, and then integrating jQuery design tools into a complete sample web site. Exercise files accompany the course.

Topics include:
  • Constructing jQuery selectors and filters to gather information from web pages
  • Creating, inserting, and manipulating web page content
  • Understanding jQuery statement chaining
  • Building event handlers that work across browsers
  • Working with jQuery effects, such as showing, hiding, and fading page elements
  • Creating custom animations with specialized properties and options
  • Using the jQuery UI plug-in to give pages a polished look
Subjects:
Developer Mobile Apps Web Mobile Web Web Development
Software:
Ajax jQuery jQuery Mobile
Author:
Joe Marini

Using global AJAX event handlers

The jQuery AJAX library provides a set of global AJAX event handlers that you can use to register functions to listen in for interesting events that take place during the lifecycle of an AJAX request on a given page. Here in the API documentation let's go ahead and click on the global AJAX event handlers, and you can see that there is about a half dozen functions that you can use to register events for when something interesting happens in an AJAX request. Now again, these are not functions that you call; these are functions that get called for you.

And so for example, you use the AJAX send function to register an event handler that gets called when an AJAX request is about to be sent. And again, these are global, so these are for all of the AJAX requests on your page. So for example, you might use the ajaxStart and ajaxComplete events to show some kind of user interface on your webpage to let the user know that there is an AJAX request taking place, and that they need to be patient while data is retrieved from the server.

You might use, for example, the ajaxError event handler to centralize all of your error handling rather than attach individual error functions to each one of your requests. Let's take a look at these events in action. We're going to jump over to the code here, and here in my code I've got Globals_Finished up in my editor, and that's this file right here. So you can see that I've got a whole bunch of functions. There is Start. There is Stop. There is Send, Complete, Error, and Success.

So I've registered functions, and basically what I am doing in each one of these functions is just using the developer console to log some message about something happening with AJAX. And then after all of these global event handlers have their functions registered, I call this get data function right here. And getData, all it's doing is using the get shorthand method to get the testdata.txt file, which we've been using in this chapter, and there is a successFn right here. And in the successFn we just simply log out that the result is being set, and we put the contents of the result parameter right here, into this content paragraph right here.

So let's save that. Let's bring this up in the browser, and let's see what happens. So I am going to run this in my local server. So you can see that "This is some text data." got set into that paragraph. Let's bring up the Developer Tools, and let's switch over to the Console, and you can see that in the order in which things happened, each one of those event handlers put out a little string to the Developer Console. So right here we have AJAX is starting and then it says About to request data and then Setting the result and then it says Looks like everything worked! Everything's finished! The AJAX request ended.

And if we go back to the code--let's scroll up-- you can see that those strings correspond to each one of these functions. So for ajaxStart it says AJAX starting, and then ajaxStop it says AJAX request ended and so on and so forth. Using these global event handlers, you can register events that will get called for every single AJAX request. In fact, let's take a look at what happens when an error occurs, and we have our ajaxError handler right here. And this function takes some parameters. So do the other ones as well, but they're optional, and I'm not using them in this example.

But here in the case of ajaxError, we have parameters for the event, the jqXHR object, any of the AJAX settings, and the actual error that happened. So let's scroll down, and make a request for a file that we know doesn't exist, right. So testdata1.txt is not real, so let's save that and then let's go back to the browser, and now let's refresh the page, and you can see that it didn't work. When we bring up the Developer Tools, right here we have our AJAX starting. It says About to request data, but then you could see that there was an error.

It seems like requesting testdata1.txt was a problem. If we expand that out, we can see that there was a whole bunch of things that took place in here, right, and then it says, Hmmm. seems that there was a problem and then not found. But you can still see that Everything's finished! and AJAX request ended functions still completed. So let's go back to the code. In this case, rather than the ajaxSuccess function being called that says looks like everything worked, this time the AJAX error function got called and it says Hmm.

Seems Like there was a problem, and the not found message is passed in by jQuery as the error of why things went wrong. These global event handlers in many ways provide some nice centralization of AJAX functionality so that you can provide some really great user experience to your users like global settings of showing when requests are in progress, or centralized error handling, and it really makes working with AJAX and jQuery a lot easier.

Find answers to the most frequently asked questions about jQuery Essential Training.


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Q: When attempting to download jQuery, as the author does in the movie “Downloading and installing jQuery,” the file does not download. When any of the links on the download page are clicked, the browser opens a page of code instead.
A: This sometimes happens when a web browser doesn't have the proper MIME type to prompt the user to download the file instead of open it directly. Therefore, the browser is opening the code instead of downloading it. If this occurs, download the file on a by Control-clicking (Mac) or right-clicking (Windows) on the download link and choosing the Save File option, which will download it to the computer.
Q: Why do some of the examples use the form $("document") instead of just $(document)?
A: jQuery's $(document).ready() function will work with either form. As a reminder, you can also just use the $() shorthand to accomplish the same thing:
 
$(function() {
// code to run when the document is ready
});
Q: I am stuck on the first exercise in Chapter 1, video 3 "Creating a simple jQuery enabled page".

Your example javascript code, both in the movie and in the exercise files,
reads as follows:

<script type="text/javascript">
$("document").ready(function() {
alert("The page just loaded!");
});
</script>

This is not working for me.
A: After jQuery 1.3.2, a change was made where quotes were no
longer needed around the "document" argument to the jQuery $() function.

Type the following instead.

<script type="text/javascript">
$(document).ready(function() {
alert("The page just loaded!");
});
</script>
Q: How do I remove the resize handle that appears on on <textarea> elements in some browsers, such as Firefox and Chrome?
A: Some browsers automatically provide this feature for these text elements. You can disable this feature using CSS by providing a style rule for the element that specifies no resize behavior. Add the rule "resize: none;" to a stylesheet that is applied to the textarea, and the resize handle will not appear.

Q: This course was updated on 5/24/2013. What changed?

A: This update includes a new chapter on the jQuery AJAX features, new movies on associating data with page elements, and updates to the chapters on events and the jQuery UI plugin to reflect changes in JQuery 1.8.
Q: In Chapter 7, for the "Using the Resizable effect" movie, the example code from the Groundswell_Final and Groundswell_Start folders isn't limiting the width of the window. What should I do?
A: There's a bug in the example file. You need to add: 
textarea { resize:none;}

to the main.css file in the _css folder, and change the link tag in register.htm from:

<link href="../_css/sunny/jquery-ui-1.7.2.custom.css" rel="stylesheet" type="text/css" media="screen, projection" />

to

<link href="../_css/sunny/jquery-ui-1.10.2.custom.css" rel="stylesheet" type="text/css" media="screen, projection" />

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