JQuery_ Novice to Ninja - Earle Castledine [14]
If the alert shows 0, you’ll know there’s a mistake in your selector. A good way to troubleshoot this sort of issue is to reduce your selector to the smallest, simplest one possible.
In our example, we could simply write $('#celebs'), which would select just the table element and alert a length of 1. From here you can make your selectors more specific, and check that you’re selecting the correct number of elements as you go.
Filters
With the knowledge that we’ve successfully selected all of the table rows, narrowing our selection down to every other row is simple—because jQuery has a filter to do it. A filter removes certain items, and keeps only the ones we want. You’ll acquire a feel for what can be filtered as we work through some more examples, but for now we’ll just jump straight to the filter we need for our zebra stripes:
chapter_02/04_filters/script.js
$(document).ready(function() {
alert($('#celebs tbody tr:even').length + ' elements!');
});
Filters are attached to the item you want to filter (in this case, the table rows) and are defined by a colon, followed by the filter name. The :even filter used here keeps every even-indexed element in the selection and removes the rest, which is what we want. When we alert the selection length now, we see 3, as expected. All of our odd-numbered rows have been filtered out of the selection. There is a wide array of jQuery selector filters available to us: :odd (as you might expect), :first, :last, :eq() (for selecting, for example, the third element), and more. We’ll look at each of these in more detail as we need them throughout the book.
Selecting Multiple Elements
One last trick for basic selecting is the ability to select multiple elements in a single statement. This is very useful, as we’ll often want to apply the same action to several elements in unrelated parts of the page. Separating the selector strings with commas allows you to do this. For example, if we wanted to select every paragraph, div element, h1 heading, and input box on the page, we’d use this selector:
$('p,div,h1,input')
Learning how to use all these different selectors together to access exactly the page elements you want is a big part of mastering jQuery. It’s also one of the most satisfying parts of using jQuery, since you can pack some fairly complex selection logic into a single short line of code!
Becoming a Good Selector
Selecting may seem quite easy and, up to a point, it is. But what we’ve covered so far has only just scratched the surface of selecting. In most cases the basics are all you’ll need: if you’re simply trying to target an element or a bunch of related elements, the element name, id, and class are the most efficient and easiest ways to achieve this.
When moving around the DOM from a given element, the situation becomes a little trickier. jQuery provides a myriad of selectors and actions for traversing the DOM. Traversing means traveling up and down the page hierarchy, through parent and child elements. You can add and remove elements as you go, applying different actions at each step—which lets you perform some mind-bogglingly complex actions in a single jQuery statement!
If you’re a wiz at CSS, you’ll already be familiar with a lot of the statements; they’re mostly borrowed directly from the CSS specification. But there are probably a few that you’re unfamiliar with, especially if you’ve yet to spend much time learning CSS3 selectors. Of course, we’ll be covering and learning advanced selection techniques as we implement them in our examples and demos. For this reason, any time you want to find out more about all the jQuery selectors available, you can just head over to the online documentation and browse away!
Decorating: CSS with jQuery
Selecting elements in jQuery is the hard part. Everything else is both easy and fun. After we have selected our targets, we are able to manipulate them to build effects or interfaces. In this section we will cover a series of jQuery actions relating to CSS: adding and removing styles, classes, and more. The