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jQuery Essential Training
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Child, visibility, and content filters


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jQuery Essential Training

with Joe Marini

Video: Child, visibility, and content filters

We are going to look now at Content and Visibility filters as well as Child filters. Content and Visibility filters examine the content of the elements that are returned by the selector expression or their visibility property to determine if they should be included or excluded from the result set. So the Content filter has four options. There is the contains filter, and you pass it some text. What will happen here is jQuery will look inside the child elements of the element on the selector to see if they contain this text string anywhere within their content, in any of their child elements.
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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

Child, visibility, and content filters

We are going to look now at Content and Visibility filters as well as Child filters. Content and Visibility filters examine the content of the elements that are returned by the selector expression or their visibility property to determine if they should be included or excluded from the result set. So the Content filter has four options. There is the contains filter, and you pass it some text. What will happen here is jQuery will look inside the child elements of the element on the selector to see if they contain this text string anywhere within their content, in any of their child elements.

The next one, the empty filter, says only include elements in the result set that have no child elements inside them. The next one, the has filter, you pass that a selector and this will filter elements in the result set that contain at least one element that matches this selector that you have given it. Finally, there is a parent content filter that says only match elements in the result set that are themselves parents. For example, they contain at least one other elements including text elements.

For the Visibility filter there are only two options. There is visible and there is hidden, and that's pretty self-explanatory. This only includes elements that are visible; this one only includes elements that are hidden. Let's take a look at the Child filters. Child filters allow you to refine the selection by looking at the relationship that the element has with its parent elements. There are four options here. Actually there are more, because the nth-child option has a few. So the nth-child filter has a couple of different things you can do. You can give it even or odd.

It kind of works the same way as the even or odd filters that we looked at in the previous example. Only in this case it's operating on child elements, not the parent elements. So this will only match elements that are even or odd inside the parent. The nth-child, where you are given an index, will match all elements that are at that index inside the parent. Then the last one, which is pretty powerful, is the equation. You can actually give nth-child an equation of the form xn+m and m is option obviously.

For example, you can say 2n for every second one or you can say 3n+1 and then n will start counting at 0. It will count 0, 1, 2 and so on. Then this equation will be calculated and then that will be the index of the element that gets selected. We will see an example of that in a moment. Then finally, there are a few other options. There is first-child, which will match elements who are the first child of their parent, and then predictably there is last and only and those will match elements who are the last child of their parent or the only child of their parent.

Back in the folder for the examples, I am going to start off with the ChildVisCont_start file, and here is the finished example if you want to jump ahead. So I am going to open this up with my text editor. This is the example file at we are going to be using for the Child and Visibility and Content filters. So let's go ahead and get started playing around with some of the examples. Let's try something pretty simple. I am going to write a query that says get me paragraph tags, only paragraphs that contain the text string 3.

Again we are going to draw our little CSS trick to make it visible and we will give it a border that's 3 pixels solid red. So let's save that and let's bring that up in the browser. When you look very quickly, you will see that there is a text string 3 right there for this guy, so that's the one that should be selected, because where paragraphs that contain 3. Save, and we are going to bring up it in the browser and you can see that that's the guy that got highlighted.

All right, let's go back to the code and make a quick change and watch what happens. First, that guy was misnumbered. Now let's take off the p. Let's just do this. Let's just do contains by itself. So what this is going to say is I don't care what element it is. Just select all the elements that contain the text string 3. Now at first blush you might say okay. Well, that's going to be this guy here, right, the list item and it's going to be this paragraph. So let's watch what happens when we go out to the browser. I am going to save.

Now I am going to refresh. Wow! Everything got selected. So the list item here that has the 3 in it and the ul right, then it looks like the entire container here, the body. And here the paragraph has a 3. So let's go figure out what's happening. So here we are back in the code. Remember what we are asking jQuery now to do is say, hey, get all the elements that contain the text string 3. Well, sure, the list item contains the text string 3, but so does the ul. Why? Because the ul contains the li and that contains that string.

Well, so is the body, and in fact you can see here that's the reason why the whole body is being outlined is because even though this paragraph right here has the string in it. Well, so does its parent and its parent is the body tag, and the parent of the body is the HTML. Everything is being highlighted. So this is an example of where results may be a little unexpected, if you are not keeping in line to the hierarchical relationship that jQuery looks at when it's examining tags. So to limit what happens when you are using filters like Contains or so on, you might want to put the scope in there that you are looking at.

So for example, if you only wanted the list item in the paragraph, we can say li:contains(3),p:contains(3), then that will do the right thing. Let's move on to the next example. So I will comment that guy, and copy and paste and uncomment. Now let's try the parent operator. So we are going to get paragraphs that are parents. So this will look at all the paragraph tags and if they contain another tag, then including text items, they will be included in the result set.

So I am going to save and then refresh, and you can see that all the paragraphs got selected because they all contained content. So they were all bordered. Now let's go back to the code. Let's try another example. Comment that guy, put this one in. Now let's try an example of the has operator. So let's get rid of this. We are going to ask jQuery to find us unordered lists and we are only going to look for unordered lists that has a list item in them that has a class attribute that's equal to a.

So what we are doing here is this is selector all on its own, so list items that have a class equal to a, but we are not selecting the list items, what we are selecting is the ul. But we are only selecting the ul, if it has a list item inside that matches this. So let's save and go back to the browser. So now we are going to refresh, and you can see that the ul was in fact included in the results, because it does have a list item that has that class.

So if we go back to the code, and we change that to class=c. Well, there is no class c. So now this will result in nothing being highlighted. So we will save, go back to the browser. Now we will refresh and you will see that the unordered list is not highlighted anymore. Let's do a couple of nth-child examples. So let's go back to the code and let's comment this and paste. So now we are going to do this. Let's say we are going to look for the, unordered list and we are going to look for the list item that's the nth child = 3.

So this says get me the list item that is the third child that's inside an unordered list. Let's go back to the browser, and refresh, and you will see that sure enough the third child is highlighted, because that's the third list item that's inside the ul. Let's go back and try something else. Let's just try now. Let's just say li:last-child and we will save and we will refresh. Let's bring it up and sure enough, the last list item child is selected.

Finally, let's try an equation. Let's comment this guy out and we will do this. Let's try, ul li:nth-child, but in this case let's do (2n). So now what's going to happen is n is going to start out counting and it's going to select every other one. So let's refresh in the browser and you can see that items 1 and 3 were selected.

That's something worth noting. So let's go back to the code. Earlier, you might have caught it when I said that jQuery operates on elements that are 0 index based. This is an exception here. When you are using the nth-child operator and you are using the equation, the n variable starts off counting at 1. It doesn't start off counting at 0. So that's something to keep in mind. But you can see that it has selected pretty much every other one in the bunch. So if I changed this to 3n, and when you refresh you can see that it's 1, 2, and 3.

So 3 time 3n is 3. That's the one that got selected. So that's how Child and Content Visibility filters work. Let's move on now to our next lesson.

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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