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jQuery Essential Training
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Associating data with page elements


From:

jQuery Essential Training

with Joe Marini

Video: Associating data with page elements

jQuery provides a couple of very useful methods for associating arbitrary data with elements on the page. There are several scenarios where this is pretty useful. For example, you might have an image on a page, and you might want to associate some data with that image such as who the photographer is, and when and where the photo was taken. Or maybe you have a series of div elements on a page, and each one of those divs contain some information about, say, an employee record, and you want to associate some data at runtime such as the employee name and their position and so on.
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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 features in jQuery
      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 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 Web Web Design Web Development
Software:
jQuery
Author:
Joe Marini

Associating data with page elements

jQuery provides a couple of very useful methods for associating arbitrary data with elements on the page. There are several scenarios where this is pretty useful. For example, you might have an image on a page, and you might want to associate some data with that image such as who the photographer is, and when and where the photo was taken. Or maybe you have a series of div elements on a page, and each one of those divs contain some information about, say, an employee record, and you want to associate some data at runtime such as the employee name and their position and so on.

jQuery makes that really easy, by providing a couple of methods that are used for working with data. So, here on the jQuery site, I'm going to jump over to the API documentation, and that takes me to api.jquery.com. And I am going to search for data, or alternatively, I can also just scroll down here to the Data category. Either one of those works. And here is the method we are going to look at. We're going to look at the data method. Now the data method is used to store and retrieve data associated with elements on the page, and there's two ways of calling it.

This group right here with the key and the value, and this instance here, the object, that's how you store data on a page element, and then the second group down here is how you retrieve the data. Now, the way data is stored is by keys and values. So for example, in the first way of calling it here, you give it a string, which is the key that you want to associate the data with, and then the value is any JavaScript object. It can be a number, it can be a string, it can be an array, it can be a complex JavaScript object. Or you can just give it an Object which contains a whole bunch of key-value pairs to put the data into the page element.

Then the other method we want to look at is the removeData method. So, let's go back down here. removeData is how you remove data from an element or set of elements on the page. Again, you can give it the element to remove the data from, and if you want, you can give it an optional string, which is the individual key for the data you want removed. Or if you just don't provide any key name at all, then all of the data will be removed. So, let's jump over to the Example Files folder.

I have got my data_start.html page right here, and this is the file we're going to use to exercise these methods. So, I am just going to double-click on it and bring it up in the browser, and you can see I've a DIV here on the page with some buttons that are going to associate and otherwise exercise our data method. Let's go over to the code and write the code for this example. Here we were on the code for that file. This is my data_start file. Here is my reference to jQuery library.

Here are the buttons down here that are going to trigger each one of these methods. Now, we haven't yet covered how to associate events with elements in jQuery, and we will see how to do that later. So, don't pay too much attention right now to these click functions. How these work will become clear later on in the course. All you need to know is that's how I am going to attach event handlers to each one of these buttons to exercise the methods I am going to be showing. All right! So, for the first one what we're going to do is when the user clicks on the store button, we want to store data with the div.

So, here in the event handler for the store button, let's just go ahead and write some code to do that. We're going to get the element, which is I believe div1, so I'll give it the id for div1. That's this id right here. So, will get #div1, and we will say .data, and we will give it a key, and I'll just use the name key1. Then we have to give it the data we want associated with the div and I'll just give it a number 1234.

We will store another piece of data on a different key, so we'll do the same thing. We will say data. And in this case I'll call it key2, and this time I'll give it a string. I'll just use my name. Okay, so that's how we store data on the div element. What's going to happen is the button will be clicked and then for these two keys, we will just store some arbitrary data, and then our program can use this data however it sees fit. To remove the data when the user clicks on the remove button, we're going to get a reference to our div, and we'll just simply call removeData.

That will remove any of the data that is on the div. Finally, we have to have some way of making sure this is all working. I'm going to have a function here in the show event handler that's going to just display a couple of alerts to see if there's any data. So, we will just say alert. We will get the div here, so that's div1. This time we're going to call the data function, and we're going to pass in the name of the key that we're interested in, but we're not going to pass in any other parameters, because now we want to retrieve the data.

We don't want to set the data. We'll get the value for key1, and then we will just copy this line and do the same thing for key2, and that should be good. All right! Let's go back to the browser and refresh the page and see if it works. I am going to refresh the page here. First I'm going to click show data without having set anything, right? And you can see that when I do that I get an alert that has undefined in it, and another one says undefined. That's because I haven't stored the data yet. Let's go ahead and click store data. Now the data has been stored on the div.

Now let's click the Show button one more time. We can see that's the first piece of data. That's the 1234 that I set. That was the number I supplied, and then the next one is my name. OK. So now let's click the Remove button, so now the data has been removed from the div and when we click this, once again we're back to undefined. OK. Let's do one more thing. Let's show how you can work with data attributes. This is a new feature in HTML5.

Data attributes basically allow you to put data directly on elements inside a page. The way you do that is right here on the div, I'm going to come down here to the div and I am going to give it an attribute. I am going to name it data-key3. I'm going to give it a value of, I don't know, I'm just going to say data attribute. These data attributes, which begin with data-, and this is a part of the HTML5 specification. This allows me to associate data directly within the element, and then these data attributes will automatically show up whenever I try to use the data method in jQuery.

It will read the contents of any data attribute I have on my elements and make them available to me via the data method. Let's try that out. Let's go back up the show function, and let's comment these two lines, put in another line, and this time what we're going to do is I'm going to say alert. We're going to say let's get the ("#div1"). We're going to get the data() method. And now we're going to call it with no arguments whatsoever, because now we want to get all of the data that's associated with the element.

So, we'll close that off and we'll save and we will go back to the browser. All right, back here in the browser, I am going to refresh. Now, I haven't stored any data yet, but watch what happens. When I click show data, you see okay, there is an object that's on the element, and it's showing up as an object in the JavaScript alert. So, let's go back to the code and make it show up as a string. Okay, so back here in the code, I'm going to take that object and I am going to show it as a string.

And the way that you do that is you can use the browser's built-in JSON object. So, I am just going to type JSON and I am going to write stringify, okay. We will give it the data element, and it takes a couple of other parameters. So the first one is going to be what's called a replacer element, and I am not going to use it, I am just going to pass in null, and then I am going to pass in a couple of spaces, which will cause the JavaScript object to be converted into a string and pretty printed with these spaces.

All right, I'll save. Back to the browser, refresh, click on show data, and you can see now that the key3 attribute, which is already in the source code, has a string value of data attribute. And notice that the data- part of the key name is stripped off. That's not part of the actual attribute name; that's just what the browser uses to indicate that something is a data attribute. So everything following the data- is what the actual attribute of the data is when it's put into the data handling method of jQuery.

So, let's click OK. Now, I'm going to store the data, like I did the first time around. You'll see that when I click show data, the key that's already on the element via the data attribute is there, along with the two keys that I added via the JavaScript code. All right! So, that's how you can associate arbitrary data with page elements using the jQuery data methods.

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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