Learning jQuery

The topic of optimization has come up a number of times in the jQuery mailing list. jQuery’s DOM traversal is powerful and easy, but it can sometimes be slow as well. As with any JavaScript library or framework, the helper methods will be slower than the plain old JavaScript (p.o.j) methods. Nevertheless, if we keep in mind the jQuery’s speed hierarchy, the speed difference between jQuery and p.o.j. will often be negligible.

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After I wrote a couple entries (Fancy Drop Cap, Part 1 and Part 2) on creating a drop cap for the first paragraph in a DIV, a couple people asked how one would go about making the drop cap apply to every paragraph in a DIV.

Most of the code can remain the way we left it in Fancy Drop Cap – Part 2. We created a swap_letter() function to:

1. find the first letter of the paragraph
2. concatenate that letter with the rest of an image tag if it matches one of the letters in a regular expression
3. strip the letter out of the paragraph since we want to replace it with the image
4. prepend the image tag to the paragraph

We also gave the image a class name of “fancy-letter” so that we could style it a bit:

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A couple weeks ago I wrote about traversing the DOM with jQuery’s selector expressions to get any elements in the document (see How to Get Anything You Want – part 1). This time around, I’m going to focus on jQuery methods that provide even more ways to get elements. Some of these methods have a nearly identical counterpart among the selector expressions, but for the most part, the two ways of getting elements complement each other.

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With jQuery, you can get to just about anything on a web page. In this entry, I’ll show you a few ways you can use jQuery’s versatile selector expressions to traverse to an element — or group of elements — in the DOM.

I’ve put together a short paragraph and an ordered list scattered with inline elements such as <em>, <code>, and links. It’s all wrapped in a DIV with an ID of “jqdt,” which allows me to focus the demonstration to one area of this page.

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With all the fun new things you can do using jQuery and other JavaScript libraries, people are using links ("a" tags) for much more than sending users to a different page. One little annoyance I've found when using links for these events, though, is the little dotted outline that appears around the linked words upon clicking them and making them "active."

It makes sense to see the outline when clicking, but I don't want it to stay there.

In Firefox 1.5 and up, it's easy to get rid of the outline with a little CSS:

Unfortunately, that doesn't work in Internet Explorer 6 and below (is anyone surprised?).

Wouldn't it be nice to get rid of the outline in every browser (as long as JavaScript is enabled, of course)?

jQuery to the Rescue

The trick is to take the focus off the link once it has been clicked, and jQuery makes that simple. In the jQuery Discussion List, Klaus Hartl offered this snippet, which works perfectly:

Or, if you wanted to apply the blur only to links inside a DIV with an ID of "magic," for example, you could replace $('a') with $('#magic a'). If the blur should apply only to links with a class of "fun," the selector would change to $('a.fun'). See how easy? Give it a try:

click me and I won't show the ugly dotted outline

For this little demo, I gave the link a class of "fun" and put the above jQuery code inside $(document).ready() (For more on $(document).ready(), see Introducing $(document).ready() ). I also added return false; because I didn't want the link to take you anywhere.

In Fancy Drop Cap - Part 1, I showed how I used jQuery to insert a drop cap on my personal weblog. But there is still some unfinished business to take care of:

1. Accounting for cases in which the first paragraph (where I want my drop cap to go) starts with another tag of some sort (<a href="...">, <em>, etc.)
2. Adding a little CSS to the drop cap

So let's begin with item 1. As you may recall, we defined three variables, first_paragraph, first_letter, and text. The variables allowed us to get the value of the textNode of the first letter of the first paragraph, so we could replace it with the image. Here is what that part looked like:

The only problem with that code is that line 3 assumes that the first child node of the first paragraph is actually a text node. But what if it's a span tag (<span>) or a link (<a href="...">)? Well, in that case we'll need to keep drilling down through the nodes until we can't go any farther.

Loop the Loop

To do that, we'll set an intermediate variable, called node, initially making it the same as first_paragraph:

Next, we change our node variable to be defined as the first child of that node (node = node.firstChild), and we keep doing that until there are no more child nodes left, by using a "while" loop:

So, in other words, as long as there is a child node, our variable will be reset as that child node.

The First Letter — and Only a Letter

When that's all done, we set our text variable, this time as the value of our node variable:

Now all we have to do is get the first letter of the text so that we can replace it with the drop-cap image: var first_letter = text.substr(0,1).

There is just one more thing that we should account for Read the rest of this entry »