Learning jQuery 1.3It began as a labor of love back in 2005 by John Resig, a JavaScript wunderkind who now works for the Mozilla Corporation. Inspired by pioneers in the field such as Dean Edwards and Simon Willison, Resig put together a set of functions to make it easy to programmatically find elements on a web page and assign behaviors to them. By the time he first publicly announced his project in January 2006, he had added DOM modification and basic animations. He gave it the name jQuery to emphasize the central role of
finding, or “querying,” parts of a web page and acting on them with JavaScript.

In the few short years since then, jQuery has grown in its feature set, improved in its performance, and gained widespread adoption by some of the most popular sites on the Internet. While Resig remains the lead developer of the project, jQuery has blossomed, in true open-source fashion, to the point where it now boasts a core team of top-notch JavaScript developers, as well as a vibrant community of thousands of developers.

The jQuery JavaScript Library can enhance your websites regardless of your background. It provides a wide range of features, an easy-to-learn syntax, and robust cross-platform compatibility in a single compact file. What’s more, hundreds of plug-ins have been
developed to extend jQuery’s functionality, making it an essential tool for nearly every client-side scripting occasion.

Learning jQuery provides a gentle introduction to jQuery concepts, allowing you to add interactions and animations to your pages—even if previous attempts at writing JavaScript have left you baffled. This book guides you past the pitfalls associated with AJAX, events, effects, and advanced JavaScript language features, and provides you with a brief reference to the jQuery library to return to again and again.

What This Book Covers

In Chapter 1 you’ll get your feet wet with the jQuery JavaScript library. The chapter begins with a description of jQuery and what it can do for you. It walks you through downloading and setting up the library, as well as writing your first script.

In Chapter 2 you’ll learn how to use jQuery’s selector expressions and DOM traversal methods to find elements on the page, wherever they may be. You’ll use jQuery to apply styling to a diverse set of page elements, sometimes in a way that pure CSS cannot.

In Chapter 3 you’ll use jQuery’s event-handling mechanism to fire off behaviors when browser events occur. You’ll see how jQuery makes it easy to attach events to elements unobtrusively, even before the page finishes loading. And, you’ll be introduced to more
advanced topics, such as event bubbling, delegation, and namespacing.

In Chapter 4 you’ll be introduced to jQuery’s animation techniques and see how to hide, show, and move page elements with effects that are both useful and pleasing to the eye.

In Chapter 5 you’ll learn how to change your page on command. This chapter will teach you how to alter the very structure of an HTML document, as well as its content, on the fly.

In Chapter 6 you’ll discover the many ways in which jQuery makes it easy to access server-side functionality without resorting to clunky page refreshes. In the next three chapters (7, 8, and 9) you’ll work through several real-world examples, pulling together what you’ve learned in previous chapters and creating robust jQuery solutions to common problems.

In Chapter 7, “Table Manipulation,” you’ll sort, sift, and style information to create beautiful and functional data layouts.

In Chapter 8, “Forms with Function,” you’ll master the finer points of client-side validation, design an adaptive form layout, and implement interactive client-server form features such as autocompletion.

In Chapter 9, “Shufflers and Rotators,” you’ll enhance the beauty and utility of page elements by showing them in more manageable chunks. You’ll make information fly in and out of view both on its own and under user control.

Chapters 10 and 11 take you beyond the core jQuery methods to explore third-party extensions to the library, and show you various ways you can extend the library yourself.

In Chapter 10, “Using Plug-ins,” you’ll examine the Form plug-in and the official collection of user interface plug-ins known as jQuery UI. You’ll also learn where to find many other popular jQuery plug-ins and see what they can do for you.

In Chapter 11, “Developing Plug-ins,” you’ll learn how to take advantage of jQuery’s impressive extension capabilities to develop your own plug-ins from the ground up. You’ll create your own utility functions, add jQuery object methods, write custom selector expressions, and more.

Effects

If actions speak louder than words, then in the JavaScript world, effects make actions speak louder still. With jQuery, we can easily add impact to our actions through a set of simple visual effects, and even craft our own, more sophisticated animations.

jQuery effects certainly add flair, as is evident when we see elements gradually slide into view instead of appearing all at once. However, they can also provide important usability enhancements that help orient the user when there is some change on a
page (especially common in AJAX applications). In this chapter, we will explore a number of these effects and combine them in interesting ways.

Inline CSS modification

Before we jump into the nifty jQuery effects, a quick look at CSS is in order. In previous chapters we have been modifying a document’s appearance by defining styles for classes in a separate stylesheet and then adding or removing those classes with jQuery. Typically, this is the preferred process for injecting CSS into HTML because it respects the stylesheet’s role in dealing with the presentation of a page. However, there may be times when we need to apply styles that haven’t been, or can’t easily be, defined in a stylesheet. Fortunately, jQuery offers the .css() method for such occasions.

This method acts as both a getter and a setter. To get the value of a style property, we simply pass the name of the property as a string, like .css(‘backgroundColor’). Multi-word properties can be interpreted by jQuery when hyphenated, as they are
in CSS notation (background-color), or camel-cased, as they are in DOM notation (backgroundColor). For setting style properties, the .css() method comes in two flavors—one that takes a single style property and its value and one that takes a map of property-value pairs:

	.css('property','value')
	.css({property1: 'value1', 'property-2': 'value2'})

Experienced JavaScript developers will recognize these jQuery maps as JavaScript object literals.

	Numeric values do not take quotation marks while string values do.
	However, when using the map notation, quotation marks are not required
	for property names if they are written in camel-cased DOM notation.

We use the .css() method the same way we’ve been using .addClass() —by chaining it to a selector and binding it to an event. To demonstrate this, we’ll return to the style switcher example of Chapter 3, but with different HTML:

	<div id="switcher">
		<div class="label">Text Size</div>
		<button id="switcher-default">Default</button>
		<button id="switcher-large">Bigger</button>
		<button id="switcher-small">Smaller</button>
	</div>
	<div class="speech">
		<p>Fourscore and seven years ago our fathers brought forth
		   on this continent a new nation, conceived in liberty,
		   and dedicated to the proposition that all men are created
		   equal.</p>
	</div>

By linking to a stylesheet with a few basic style rules, the page can initially look like the following screenshot:

In this version of the style switcher, we’re using elements. Clicking on the Bigger and Smaller buttons will increase or decrease the text size of

, while clicking on the Default button will reset

to its original text size.

If all we wanted were to change the font size a single time to a predetermined value, we could still use the .addClass() method. But let’s suppose that now we want the text to continue increasing or decreasing incrementally each time the respective button is clicked. Although it might be possible to define a separate class for each click and iterate through them, a more straightforward approach would be to compute the new text size each time by getting the current size and increasing it by a set factor (for example, 40%).

Our code will start with the $(document).ready() and $(‘#switcher-large’). click() event handlers:

	$(document).ready(function() {
		$('#switcher-large').click(function() {
		});
	});

Next, the font size can be easily discovered by using the .css() method: $(‘div.speech’).css(‘fontSize’). However, because the returned value will include a trailing ‘px’, we’ll need to strip that part in order to perform calculations with the value. Also, when we plan to use a jQuery object more than once, it’s generally a good idea to cache the selector by storing the resulting jQuery object in a variable
as well.

	$(document).ready(function() {
		<b>var $speech = $('div.speech');</b>
		$('#switcher-large').click(function() {
			<b>var num = parseFloat($speech.css('fontSize'), 10);</b>
		});
	});

The first line inside $(document).ready() now stores a variable for

itself. Notice the use of a $ in the variable name, $speech. Since $ is a legal character in JavaScript variables, we can use it as a reminder that the variable is storing a jQuery object.

Inside the .click() handler, we use parseFloat() to get the font size property’s number only. The parseFloat() function looks at a string from left to right until it encounters a non-numeric character. The string of digits is converted into a fl oating-point (decimal) number. For example, it would convert the string ’12’ to the number 12. In addition, it strips non-numeric trailing characters from the string,
so ’12px’ becomes 12 as well. If the string begins with a non-numeric character, parseFloat() returns NaN, which stands for Not a Number. The second argument for parseFloat() allows us to ensure that the number is interpreted as base-10 instead of octal or some other representation.

All that’s left to do, if we are increasing by 40%, is to multiply num by 1.4 and then set the font size by concatenating num and ‘px’:

	$(document).ready(function() {
		var $speech = $('div.speech');
		$('#switcher-large').click(function() {
			var num = parseFloat($speech.css('fontSize'), 10 );
			<b>num *= 1.4;
			$speech.css('fontSize', num + 'px');</b>
		});
	});

	The equation num *= 1.4 is shorthand for num = num * 1.4. We can use
	the same type of shorthand for the other basic mathematical operations,
	as well: addition, num += 1.4; subtraction, num -= 1.4; division,
	num /= 1.4; and modulus (division remainder), num %= 1.4.

Now when a user clicks on the Bigger button, the text becomes larger. Another click,and the text becomes larger still, as shown in the following screenshot:

To get the Smaller button to decrease the font size, we will divide rather than multiply—num /= 1.4. Better still, we’ll combine the two into a single .click() handler on all

elements within

. Then, after finding the numeric value, we can either multiply or divide depending on the ID of the button that was clicked. Here is what that code looks like now:

	$(document).ready(function() {
		var $speech = $('div.speech');
		<b>$('#switcher button').click(function() {</b>
			var num = parseFloat( $speech.css('fontSize'), 10 );
			<b>if (this.id == 'switcher-large') {
				num *= 1.4;
			} else if (this.id == 'switcher-small') {
				num /= 1.4;
			}</b>
			$speech.css('fontSize', num + 'px);
		});
	});

Recall from Chapter 3 that we can access the id property of the DOM element referred to by this, which appears here inside the if and else if statements. Here, it is more efficient to use this than to create a jQuery object just to test the value of a property.

It’s also nice to have a way to return the font size to its initial value. To allow the user to do so, we can simply store the font size in a variable immediately when the DOM is ready. We can then use this value whenever the Default button is clicked. To handle this click, we could add another else if statement. However, perhaps a switch statement would be more appropriate.

	$(document).ready(function() {
		var $speech = $('div.speech');
		<b>var defaultSize = $speech.css('fontSize');</b>
		$('#switcher button').click(function() {
			var num = parseFloat( $speech.css('fontSize'), 10 );
			<b>switch (this.id) {
				case 'switcher-large':
					num *= 1.4;
					break;
				case 'switcher-small':
					num /= 1.4;
					break;
				default:
					num = parseFloat(defaultSize, 10);
			}</b>
			$speech.css('fontSize', num + 'px');
		});
	});

Here we’re still checking the value of this.id and changing the font size based on it, but if its value is neither ‘switcher-large’ nor ‘switcher-small’ it will default to the initial font size.

Basic hide and show

The basic .hide() and .show() methods, without any parameters, can be thought of as smart shorthand methods for ss(‘display’,’string’), where ‘string’ is the appropriate display value. The effect, as might be expected, is that the matched set of elements will be immediately hidden or shown, with no animation.

The .hide() method sets the inline style attribute of the matched set of elements to display:none. The smart part here is that it remembers the value of the display property—typically block or inline—before it was changed to none. Conversely, the .show() method restores the matched set of elements to whatever visible display property they had before display:none was applied.

	For more information about the display property and how its values are
	visually represented in a web page, visit the Mozilla Developer Center at
	https://developer.mozilla.org/en/CSS/display/ and view
	examples at https://developer.mozilla.org/samples/cssref/
	display.html.

This feature of .show() and .hide() is especially helpful when hiding elements whose default display property is overridden in a stylesheet. For example, the

•  element has the property display:block by default, but we might want to change it to display:inline for a horizontal menu. Fortunately, using the .show() method on a hidden element such as one of these
• tags would not merely reset it to its default display:block, because that would put the
• on its own line. Instead, the element is restored to its previous display:inline state, thus preserving the horizontal design.

A quick demonstration of these two methods can be set up by adding a second paragraph and a “read more” link after the first paragraph in the example HTML:

	<div id="switcher">
		<div class="label">Text Size</div>
		<button id="switcher-default">Default</button>
		<button id="switcher-large">Bigger</button>
		<button id="switcher-small">Smaller</button>
	</div>
	<div class="speech">
		<p>Fourscore and seven years ago our fathers brought forth
		   on this continent a new nation, conceived in liberty,
		   and dedicated to the proposition that all men are
		   created equal.
		</p>
		<p>Now we are engaged in a great civil war, testing whether
		   that nation, or any nation so conceived and so dedicated,
		   can long endure. We are met on a great battlefield of
		   that war. We have come to dedicate a portion of that
		   field as a final resting-place for those who here gave
		   their lives that the nation might live. It is altogether
		   fitting and proper that we should do this. But, in a
		   larger sense, we cannot dedicate, we cannot consecrate,
		   we cannot hallow, this ground.
		</p>
		<b><a href="#" class="more">read more</a></b>
	</div>

When the DOM is ready, the second paragraph is hidden:

	$(document).ready(function() {
		$('p:eq(1)').hide();
	});

And the speech looks like the following screenshot:

Then, when the user clicks on read more at the end of the first paragraph, that link is hidden and the second paragraph is shown:

	$(document).ready(function() {
		$('p:eq(1)').hide();
		<b>$('a.more').click(function() {
			$('p:eq(1)').show();
			$(this).hide();
			return false;
		});</b>
	});

Note the use of return false to keep the link from activating its default action. Now the speech looks like this:

The .hide() and .show() methods are quick and useful, but they aren’t very flashy. To add some flair, we can give them a speed.

Effects and speed

When we include a speed (or, more precisely, a duration) with .show() or .hide(), it becomes animated—occurring over a specified period of time. The .hide(‘speed’) method, for example, decreases an element’s height, width, and opacity simultaneously until all three reach zero, at which point the CSS rule display:none is applied. The .show(‘speed’) method will increase the element’s height from top to bottom, width from left to right, and opacity from 0 to 1 until its contents are completely visible.

Speeding in

With any jQuery effect, we can use one of three preset speeds: ‘slow’, ‘normal’, and ‘fast’. Using .show(‘slow’) makes the show effect complete in .6 seconds, .show(‘normal’) in .4 seconds, and .show(‘fast’) in .2 seconds. For even greater precision we can specify a number of milliseconds, for example .show(850). Unlike the speed names, the numbers are not wrapped in quotation marks.

Let ‘s include a speed in our example when showing the second paragraph of Lincoln’s Gettysburg Address:

	$(document).ready(function() {
		$('p:eq(1)').hide();
		$('a.more').click(function() {
			<b>$('p:eq(1)').show('slow');</b>
			$(this).hide();
			return false;
		});
	});

When we capture the paragraph’s appearance at roughly halfway through the effect, we see something like the following:

Fading in and fading out

While the animated .show() and .hide() methods are certainly flashy, they may at times be too much of a good thing. Fortunately, jQuery offers a couple other pre-built animations for a more subtle effect. For example, to have the whole paragraph appear just by gradually increasing the opacity, we can use .fadeIn(‘slow’) instead:

	$(do cument).ready(function() {
		$('p:eq(1)').hide();
		$('a.more').click(function() {
			<b>$('p:eq(1)').fadeIn('slow');</b>
			$(this).hide();
			return false;
		});
	});

This time when we capture the paragraph’s appearance halfway, it’s seen as:

The difference here is that the .fadeIn() effect starts by setting the dimensions of the paragraph so that the contents can simply fade into it. To gradually decrease the opacity we can use .fadeOut().

Compound effects

Sometimes we have a need to toggle the visibility of elements, rather than displaying them once as we did in the previous example. Toggling can be achieved by first checking the visibility of the matched elements and then attaching the appropriate method. Using the fade effects again, we can modify the example script to look like this:

	$(document).ready(function() {
		var $firstPara = $('p:eq(1)');
		$firstPara.hide();
		$('a.more').click(function() {
			if ($firstPara.is(':hidden')) {
				$firstPara.fadeIn('slow');
				$(this).text('read less');
			} else {
				$firstPara.fadeOut('slow');
				$(this).text('read more');
			}
			return false;
		});
	});

As we did earlier in the chapter, we’re caching our selector here to avoid repeated DOM traversal. Notice, too, that we’re no longer hiding the clicked link; instead, we’re changing the its text.

Using an if else statement is a perfectly reasonable way to toggle elements’ visibility. But with jQuery’s compound effects we can leave the conditionals out of it (although, in this example, we still need one for the link text). jQuery provides a .toggle() method, which acts like .show() and .hide(), and like them, can be used with a speed argument or without. The other compound method is .slideToggle(), which shows or hides elements by gradually increasing or decreasing their height. Here is what the script looks like when we use the .slideToggle() method:

	$(document).ready(function() {
		var $firstPara = $('p:eq(1)');
		$firstPara.hide();
		$('a.more').click(function() {
			<b>$firstPara.slideToggle('slow');
			var $link = $(this);
			if ( $link.text() == "read more" ) {
				$link.text('read less');
			} else {
				$link.text('read more');
			}</b>
			return false;
		});
	});

This time $(this) would have been repeated, so we’re storing it in the $link variable for performance and readability. Also, the conditional statement checks for the text of the link rather than the visibility of the second paragraph, since we’re only using it to change the text.

Creating custom animations

In addition to the pre-built effect methods, jQuery provides a powerful .animate() method that allows us to create our own custom animations with fine-grained control. The .animate() method comes in two forms. The first takes up to four arguments:

1. A map of style properties and values—similar to the .css() map discussed
   earlier in this chapter
2. An optional speed—which can be one of the preset strings or a number
   of milliseconds
3. An optional easing type—an advanced option discussed in Chapter 10
4. An optional callback function—which will be discussed later in this chapter

All together, the four arguments look like this:

	.animate({property1: 'value1', property2: 'value2'},
		speed, easing, function() {
			alert('The animation is finished.');
		}
	);

The second form takes two arguments, a map of properties and a map of options.

	.animate({properties}, {options})

In effect, the second argument wraps up the second through fourth arguments of the first form into another map, and adds two more options to the mix. When we adjust the line breaks for readability, the second form looks like this:

	.animate({
		property1: 'value1',
		property2: 'value2'
	}, {
		duration: 'value',
		easing: 'value',
		complete: function() {
			alert('The animation is finished.');
		},
		queue: boolean,
		step: callback
	});

For now we’ll use the first form of the .animate() method, but we’ll return to the second form later in the chapter when we discuss queuing effects.

Toggling the fade

When we discussed compound effects, did you notice that not all methods have a corresponding method for toggling? That’s right: while the sliding methods include .slideToggle(), there is no corresponding .fadeToggle() to go along with .fadeIn() and .fadeOut()! The good news is that we can use the .animate() method to easily make our own toggling fade animation. Here, we’ll replace the .slideToggle() line of the previous example with our custom animation:

	$(document).ready(function() {
		$('p:eq(1)').hide();
		$('a.more').click(function() {
			<b>$('p:eq(1)').animate({opacity: 'toggle'}, 'slow');</b>
			var $link = $(this);
			if ( $link.text() == "read more" ) {
				$link.text('read less');
			} else {
			$link.text('read more');
			}
			return false;
		});
	});

As the example illustrates, the .animate() method provides convenient shorthand values for CSS properties — ‘show’, ‘hide’, and ‘toggle’ — to ease the way when the shorthand methods aren’t quite right for the particular task.

Animating multiple properties

With the .animate() method, we can modify any combination of properties simultaneously. For example, to create a simultaneous sliding and fading effect when toggling the second paragraph, we simply add the height property-value pair to .animate()’s properties map:

	$(document).ready(function() {
		$('p:eq(1)').hide();
		$('a.more').click(function() {
			<b>$('p:eq(1)').animate({
				opacity: 'toggle',
				height: 'toggle'
				},
				'slow');</b>
			var $link = $(this);
			if ( $link.text() == "read more" ) {
				$link.text('read less');
			} else {
			$link.text('read more');
			}
			return false;
		});
	});

Additionally, we have not only the style properties used for the shorthand effect methods at our disposal, but also other properties such as: left, top, fontSize, margin, padding, and borderWidth. Recall the script to change the text size of the speech paragraphs. We can animate the increase or decrease in size by simply substituting the .animate() method for the .css() method:

	$(document).ready(function() {
		var $speech = $('div.speech');
		var defaultSize = $speech.css('fontSize');
		$('#switcher button').click(function() {
			var num = parseFloat( $speech.css('fontSize'), 10 );
			switch (this.id) {
				case 'switcher-large':
					num *= 1.4;
					break;
				case 'switcher-small':
					num /= 1.4;
					break;
				default:
					num = parseFloat(defaultSize, 10);
			}
			$speech.animate({fontSize: num + 'px'},
						'slow');
		});
	});

The extra properties allow us to create much more complex effects, too. We can, for example, move an item from the left side of the page to the right while increasing its height by 20 pixels and changing its border width to 5 pixels. So, let’s do that with the