HTML5 and CSS3, Second Edition

our pages faster. Using Google’s content-delivery network has an additional

benefit—since other sites link to the jQuery library at Google, our visitors

may already have the library cached by their browsers. As you probably

already know, browsers use a file’s full URL to decide whether it has a cached

copy. If you plan to work with jQuery on a laptop or on a computer without

constant Internet access, you’ll want to link to a local copy instead.

A2.2 jQuery Basics

Once you’ve loaded the jQuery library on your page, you can start working

with elements. jQuery has a function called jQuery(), which lets us fetch ele-

ments using CSS selectors and wrap them in jQuery objects so we can

manipulate those elements.

There’s a short version of the jQuery() function, $();, and that’s what we use in

this book. Throughout this book, I refer to this as “the jQuery function.” Here’s

how it works:

If you wanted to find the h1 tag on a page, you’d use the following:

jqueryprimer/simple_selection.html

$("h1");

If you wanted to find all of the <h1> tags on the page, you’d use the exact

same thing. If you were looking for all elements with the class of important,

you’d do this:

jqueryprimer/simple_selection.html

$(".important");

Look at that again. The only difference between it and the previous examples

is the CSS selector we used. If we were looking for the element with the id of

header, we’d simply do

varheader= $("#header");

And if we wanted to find all links within the sidebar, we’d use the appropriate

selector for that, which would be $("#sidebara").

The jQuery function returns a jQuery object, which is a special JavaScript

object containing an array of the DOM elements that match the selector. This

object has many predefined methods we can use to manipulate the elements

we selected. Let’s take a look at a few of those in detail.

A2.3 Methods to Modify Content

We use several jQuery methods to modify our HTML content as we work

through the projects in this book.

Appendix 2. jQuery Primer • 264

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