Beginning JavaScript with DOM Scripting and Ajax, 2nd Edition

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Chapter 8 ■ Back-End Interaction with Ajax and Node.js XHRtimeout.js (continued) if( request.readyState == 4 && !readrss.timedout ) { window.clearTimeout( readrss.toolong ); if( /200|304/.test( request.status ) ) { readrss.retrieved( request ); } else { readrss.failed( request ); } } } request.open('get', 'loadrss.php?url='+encodeURI( url ) ); request.setRequestHeader('If-Modified-Since', 'Mon, 12 Jan 2013 00:00:00 GMT' ); request.send( null ); return false; }, The rest of the script stays the same. A Larger Ajax Example: Connected Select Boxes Let’s take a look at a larger Ajax example—I call it that although you won’t be using XML. Connected select boxes are a classic example of what JavaScript can do for you to make an interface faster. One common use for them is the flight offer web site, where you choose one airport in a select box and the page immediately shows you the destination airports that are available from this airport in a second select box. Traditionally, this is achieved by keeping all the airport connection data in JavaScript arrays and manipulating the options arrays of the select elements. Changing the first airport select box automatically changes the second one to the available destinations. This is very nice when you have a mouse and you have JavaScript available; however, it can be pretty frustrating when one of the two is missing, or even impossible when neither is available. This example will show how you can create interdependent select boxes that work without a mouse and JavaScript and will not reload the whole page when JavaScript is available. The trick is to make the functionality work on the server side and then add the JavaScript and XHR tricks to stop the whole page from reloading. Because you don’t know whether the user really can cope with this, you can even make it optional instead of a given. ■ ■Note This approach to Ajax is more accessibility aware than the original one. The reason is that you don’t want to make the biggest DHTML mistake once again—using a technology without considering those who cannot deal with it. Jeremy Keith coined this approach HIJAX in his DOM scripting book, but so far it hasn’t gotten as much public awareness as the Ajax term has. The first step is to create a server-side script that does all the functionality. Because this is not a book about PHP, we won’t get into too much detail here. It suffices to say that the main document exampleSelectBoxes.php includes a smaller PHP script, selectBoxes.php. The latter contains all the airport data as arrays (but could as easily go to a database to retrieve them) and writes out the different states of the interface based on the user selecting a choice and sending the form, as shown in Figure 8-8. 266 www.it-ebooks.info
Chapter 8 ■ Back-End Interaction with Ajax and Node.js Figure 8-8. Connected select boxes The main page features the form with a DIV with an id you can use for the XHR output. exampleSelectBoxes.php (excerpt) ■ ■Note This example uses POST as the method to send the data. 267 www.it-ebooks.info
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Contents at a Glance About the Auth
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Chapter 1 Getting Started with Java
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Chapter 1 ■ Getting Started with
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Generating a Random Number Chapter
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Chapter 3 From DHTML to DOM Scripti
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Variable and Function Scope Chapter
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Changing Attributes of Elements Cha
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Shortening Your Scripts via InnerHT
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DOMhelp: Your Own Helper Library Ch
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Chapter 5 Presentation and Behavior
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Chapter 6 Common Uses of JavaScript
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Chapter 6 ■ Common Uses of JavaSc
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Rollover Effects on Parent Elements
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Embedded Slide Shows Chapter 6 ■
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User Feedback Methods The user feed
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APPENDIX A ■ Debugging JavaScript
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Index • A Anonymous function, 67
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■ Index • F Flash of unstyled c
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■ Index initialization method, 17
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Beginning JavaScript with DOM Scrip
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For Dad. Thanks for Saturdays full
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■ Contents The Composite Data Typ
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■ Contents Slide Shows 160 Summar
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■ Contents ■■Chapter 10: Mode
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About the Authors Russ Ferguson is
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Acknowledgments I want to thank eve
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