Learning jQuery

Last time I showed you how to make something appear and disappear on a web page. This time I'll show you how to do it with style.

Like we did last time, we'll start with our $(document).ready() and put everything else inside of it.

Adjust the Speed

This time, however, we're going to adjust the speed at which our item shows and hides. To do so, we put a speed indicator — "slow" or "normal" or "fast" or a number of milliseconds (1000 = 1 second) — inside the parentheses:

Note: If you use a speed word, put it inside quotation marks (either single or double); if you use a number, omit the quotation marks: $('#slickbox').show(500);

Attach Effects to Events

The final step here is to attach the effects to events. Last time we attached our effects to the "onclick" event of buttons. This time we'll attach them to links. But here's the rub: Links already have events attached to them. They take the user to whatever URL is indicated in the "href" attribute, usually another page. That means that we not only need to make something happen, but we also need to stop the default thing from happening. We can prevent the default behavior by adding return false;.

So let's take a look at how we would tie the "onclick" event of one link with an ID of "slick-show" to the "show" effect. Here, show() will display a DIV with an ID of "slickbox":

Notice that we attach ".click()" to "a#slick-show". In jQuery, events will often have anonymous, or lambda, functions inside them. That's why inside the parentheses of ".click()" you see function() { ... }. By the way, it's called an anonymous function because it has no name associated with it. I don't know why it's also called a lambda function. Can someone enlighten me?

Here is the final code for three effects — show(), hide(), and toggle(). I've added $('#slidebox').hide() as the first line after $(document).ready() to hide that DIV when the page loads.

Look closely at the code and you'll see that our slickbox will show at a slow speed, hide at a fast speed, and toggle somewhere in between (in 400 milliseconds).

Demo 1

Try it out for yourself. Just click on the three following links:

Show the box  Hide the box  Toggle the box

This is the box that will be shown and hidden and toggled at your whim.

Newbie Tip

For those of you brand new to JavaScript as well as jQuery, the lines of code that begin with two slashes ( // ) are comment lines that have no effect on the code whatsoever. You can also create multi-line comments by enclosing them in /* and */

Other Effects

Other simple jQuery effects for showing or hiding elements include:

• slideUp()
• slideDown()
• slideToggle()
• fadeIn()
• fadeOut()

Demo 2

Try the slide effects to see how they differ from show/hide:
Slide the box down  Slide the box up  Slide toggle the box

Bonus

For more sophisticated effects, check out Stefan Petre's Interface plugin

UPDATE

If this type of showing and hiding isn't exactly what you're looking for, please check out my other entries and Jörn Zaefferer's accordion menu plugin:

• Accordion Madness
• More Showing, More Hiding
• Slicker Show and Hide
• Basic Show and Hide
• Accordion Menu Plugin

As promised in my last entry, I'll be showing you a simple effect that you can do using jQuery: showing or hiding something, or a group of things, on the page. The two functions that let us do this are, not surprisingly, show() and hide().
jQuery also comes with another function called toggle(), which will make matching elements visible if they are hidden or hidden if they are visible.

So, let's get down to business. We're going to start with our $(document).ready() function.

Next, we'll choose what we want to show or hide. Hmm, let's see. How about the site's title? Excellent! Now, whenever we refer to an element in jQuery, we start with the dollar sign, $, and we put any CSS or XPATH selector in parentheses right after it: $('css-selector')

Since the site's title is wrapped in an <h1> tag, we'll refer to it this way: $('h1'). We could just as easily refer to all DIVs with a class of "treacle" — $('div.treacle') — or any paragraph that is a chlid of a DIV with an ID of "bonespur" — $('#bonespur > p').

Now for the magic. To make the site's title disappear, we just connect $('h1') and hide() with a dot (.) and stick it all inside the $(document).ready() like so:

The code above will make the site's title hide when the DOM / page loads, which isn't ideal for our purposes here, so I'm going to attach the the hide() event to the first button below instead. The second and third buttons will handle show() and toggle() respectively.

How did I attach the hiding and showing to those buttons? I'll show you that in my next entry.

One more great thing about $(document).ready() that I didn't mention in my previous post is that you can use it more than once. In fact, if you don't care at all about keeping your code small, you could litter your javascript file with them.

It's great to be able to group your functions within a file or even across multiple files, and jQuery's flexible $(document).ready() function allows you to do that, pain free.

You could, for example, have one .js file that is loaded on every page, and another one that is loaded only on the homepage, both of which would call $(document).ready(). So, inside the <head> tag of your homepage, you would have three references to JavaScript files altogether, like so:

You could also do something like this inside a single .js file:

A final note: In a comment to my previous post, Jörn gave this excellent tip for shrinking your code:

Even for this little amount of code is a shortcut available:

$(function() {
// do something on document ready
});

A function passed as an argument to the jQuery constructor is bound to the document ready event.

Coming Up: In my next entry, I'll show how to do a simple effect with jQuery. You'll be amazed at how easy it is!

Jörn Zaefferer has put together a nice "Getting Started Guide" that can help people, um, get started wtih jQuery. It'll help anyone who is new to jQuery, and even those who are fairly new to JavaScript and programming in general — just the kind of help I like. Here is what the guide includes:

1. Setup
2. Hello jQuery
3. Find me: Using selectors and events
4. Rate me: Using AJAX
5. Animate me: Using FX
6. Sort me: Using tablesorter plugin
7. Plug me: Writing your own plugins
8. Next steps

We'll be covering some of these topics here, too, but the more people who get the message out about how easy it is to use jQuery, the better.

This is the first thing to learn about jQuery: If you want an event to work on your page, you should call it inside the $(document).ready() function. Everything inside it will load as soon as the DOM is loaded and before the page contents are loaded.

The $(document).ready() function has a ton of advantages over other ways of getting events to work. First of all, you don't have to put any "behavioral" markup in the HTML. You can separate all of your javascript/jQuery into a separate file where it's easier to maintain and where it can stay out of the way of the content. I never did like seeing all those "javascript:void()" messages in the status bar when I would hover over a link. That's what happens when you attach the event directly inside an <a href> tag.

On some pages that use traditional javascript, you'll see an "onload" attribute in the <body> tag. The problem with this is that it's limited to only one function. Oh yeah, and it adds "behavioral" markup to the content again. Jeremy Keith's excellent book, DOM Scripting, showed me how to create an addLoadEvent function to a separate javascript file that allows for multiple functions to be loaded inside it. But it requires a fair amount of code for something that should be rather straightforward. Also, it triggers those events when the window loads, which leads me to another advantage of $(document).ready().

With $(document).ready(), you can get your events to load or fire or whatever you want them to do before the window loads. Everything that you stick inside its brackets is ready to go at the earliest possible moment — as soon as the DOM is registered by the browser, which allows for some nice hiding and showing effects and other stuff immediately when the user first sees the page elements.