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null or undefined, remove the attribute. jQuery.fn.toggleAttr = function( name, onValue, offValue, on ) { }; function set( $element, on ) { var value = on ? onValue : offValue; return value == null ? $element.removeAttr( name ) : $element.attr( name, value ); } return on !== undefined ? set( this, on ) : this.each( function( i, element ) { var $element = $(element); set( $element, $element.attr(name) !== onValue ); }); Why go to the trouble of building something so general-purpose? Now we can write similar togglers for other attributes with almost no effort. Suppose you need to do the same thing as .toggleCheck(), but now you’re enabling and disabling input controls. You can write a .toggleEnable() in one line of code: // Enable or disable every input element selected in this jQuery object. // Toggle the enable state of each one if enable is omitted. jQuery.fn.toggleEnable = function( enable ) { return this.toggleAttr( 'disabled', false, true, enable ); }; Note how the onValue and offValue parameters let us swap the true and false attribute values, making it easy to talk about “enabling” the element instead of the less intuitive “disabling” that the disabled attribute provides normally. As another example, suppose we need to toggle a foo attribute where its “on” state is the string value bar, and its “off” state is to remove the attribute. That’s another one-liner: // Add or remove an attribute foo="bar". // Toggle the presence of the attribute if add is omitted. jQuery.fn.toggleFoo = function( add ) { return this.toggleAttr( 'foo', 'bar', null, add ); }; Discussion It’s always good to beware of feeping creaturism (aka creeping featurism). If all we really needed were to toggle checkboxes, we could code the whole thing like this: jQuery.fn.toggleCheck = function( on ) { return on !== undefined ? this.attr( 'checked', on ) : this.each( function( i, element ) { var $element = $(element); $element.attr( 'checked', ! $element.attr('checked') ); 100 | Chapter 5: Faster, Simpler, More Fun
}; }); That is a bit simpler than our .toggleAttr() method, but it’s only useful for the checked attribute and nothing else. What would we do if we later needed that .toggleEnable() method? Duplicate the whole thing and change a few names? The extra work in .toggleAttr() buys us a lot of flexibility: we now can write a whole family of attribute togglers as straightforward one-liners. Check the documentation for the version of jQuery you’re using before writing new utility methods like this. It’s always possible that similar methods could be added to future versions of jQuery, saving you the trouble of writing your own. 5.8 Finding the Bottlenecks Problem Your site is too slow to load or too slow to respond to clicks and other user interaction, and you don’t know why. What part of the code is taking so much time? Solution Use a profiler, either one of the many available ones or a simple one you can code yourself. Discussion A profiler is a way to find the parts of your code that take the most time. You probably already have at least one good JavaScript profiler at your fingertips. Firebug has one, and others are built into IE 8 and Safari 4. These are all function profilers: you start profiling, interact with your page, and stop profiling, and then you get a report showing how much time was spent in each function. That may be enough right there to tell you which code you need to speed up. There are also some profilers specific to jQuery that you can find with a web search for jquery profiler. These let you profile selector performance and look more deeply at jQuery function performance. For really detailed profiling, where you need to analyze individual sections of code smaller than the function level, you can write a simple profiler in just a few lines of code. You may have coded this ad hoc classic: var t1 = +new Date; // ... do stuff ... var t2 = +new Date; alert( ( t2 - t1 ) + ' milliseconds' ); 5.8 Finding the Bottlenecks | 101
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Solutions & Examples for jQuery Dev
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jQuery Cookbook
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jQuery Cookbook by jQuery Community
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2.3 Selecting Elements by Index Ord
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8.5 Passing Dynamic Data to Event H
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16.5 Using HTML Fragments and jQuer
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This is largely what makes somethin
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on client-side optimization techniq
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Tech Editors Karl Swedberg, after h
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What You’ll Learn We’ll start o
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If none of this works, it’s possi
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800-998-9938 (in the United States
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traversing and manipulation, browse
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• Using the jQuery wrapper and im
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The jQuery wrapper set A good major
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— Attr — Class — HTML — Tex
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alert('jQuery ' + jQuery.fn.jquery)
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alert(jQuery('p').text()); }); T
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You should be aware that the first
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"4 inputs" alert('selected' + jQuer
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1.6 Finding Descendant Elements Wit
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.end().end().length); //alerts 3
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Now, let’s select the second ele
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jQuery('jQuery').find('a').attr('hr
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• While the elements selected are
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Discussion The cloning method is ac
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method by passing the method the at
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jQuery('p').text('Hello World,
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2.0 Introduction CHAPTER 2 Selectin
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It’s worth noting that combinator
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all siblings that follow, not just
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Discussion As mentioned, an element
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2.6 Selecting Elements by What They
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The preceding selector would select
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These filters can also be used with
Page 73 and 74: Solution As well as passing a selec
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Page 78 and 79: alert(urls.join(",")); We were able
Page 80 and 81: Even though this may be the most ob
Page 82 and 83: Figure 3-2. Code output As you can
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Page 86 and 87: Figure 3-4. Code output 3.4 Getting
Page 88 and 89: Discussion The core method index()
Page 90 and 91: Figure 3-6. Code output In the prec
Page 92 and 93: ligula. Aenean mattis pulvinar est
Page 94 and 95: Solution Let’s say you inherit a
Page 96 and 97: If you use this technique, you will
Page 98 and 99: available on the Web. jQuery hosts
Page 100 and 101: Discussion In the preceding example
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Page 104 and 105: }); })(jQuery); 4.3 Filtering Array
Page 106 and 107: Discussion In this example, we have
Page 108 and 109: }); }); })(jQuery); Discussion Upon
Page 110 and 111: Discussion In this recipe, we use t
Page 112 and 113: Solution The if/else statement and
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Page 116 and 117: } $('#province').toggle( value == '
Page 118 and 119: Did jQuery invent chaining? No. jQu
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Page 122 and 123: }; return object; That could also b
Page 126 and 127: The +new Date in this code is just
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Page 134 and 135: And you have this HTML code in your
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Page 138 and 139: A Warning About for..in Loops Never
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Page 146 and 147: Solution 1 You’re using the minif
Page 148 and 149: After the page loads, you are down
Page 150 and 151: 5.19 Writing Unobtrusive JavaScript
Page 152 and 153: Documentation Tutorials We’ve
Page 154 and 155: Beware that you don’t make the us
Page 156 and 157: + $(document).scrollLeft() }) .show
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