John Pollock - JavaScript: A Beginners Guide, Fourth Edition

JavaScript

A Beginners Guide

Fourth Edition

John Pollock

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To my wife Heather, daughters Eva and Elizabeth, Bruce and Joy Anderson, and Dr. J. D. and Linda Andrews

In memory of James D. and Livian Anderson, John William and Edith Hopkins, Burley T. and Aline Price, Doc Flores, and Clifton Idom

About the Author

John Pollock is employed as a Web Administrator during the day and works on Web sites and other projects during the evening. He runs a Web site devoted to Web development and design: Script the Web (www.scripttheweb.com). He also is a contributor to Web Xpertz (www.webxpertz.net), a help community for Web developers. John holds a Bachelor of Arts in English from Sam Houston State University and currently lives in Huntsville, Texas with his wife, Heather, and his daughters, Eva and Elizabeth.

About the Technical Editor

Christie Sorenson is a senior software engineer at ZingChart. She has worked on JavaScript-based systems in analytics, content management, and business applications since 1997 and has been fascinated with the evolution of the language and its users. She has collaborated on several books, including Ajax: The Complete Reference and HTML & CSS: The Complete Reference and was also the tech editor on JavaScript: The Complete Reference and HTML: A Beginners Guide. She holds a Bachelor of Science in Computer Science from University of California, San Diego, and now lives in San Francisco with her husband, Luke, and daughters, Ali and Keira.

Contents at a Glance

Contents

TheElement

Acknowledgments

I would like to begin by thanking my wonderful wife, Heather Pollock, for all of her love, support, and encouragement in all I do. I love you! I would also like to thank my two daughters, Eva and Elizabeth. I love both of you!

I would like to thank my parents, Bruce and Joy Anderson, for their love and guidance, and for always supporting my endeavors.

I would like to thank Dr. J. D. and Linda Andrews for their love, guidance, and support.

In addition I would like to thank John and Betty Hopkins (grandparents), James D. and Livian Anderson (grandparents), Clifton and Juanita Idom (grandparents), Richard Pollock (brother) and family, Misty Castleman (sister) and family, Warren Anderson (brother) and family, Jon Andrews (brother) and family, Lisa and Julian Owens (aunt/uncle) and family, and every aunt, uncle, cousin, or other relation in my family. All of you have been a great influence in my life.

I would like to thank all of my editors at McGraw-Hill/Professional for their outstanding help and support throughout the writing of this book. Thanks to Brandi Shailer, Ryan Willard, Amanda Russell, and to all of the editors who worked on each edition of the book.

Thanks to my technical editor, Christie Sorenson, for editing and checking over all of the technical aspects of the book, and helping me provide clear explanations of the topics that are covered.

I would like to thank God for the ability He has given me to help and teach people by my writing. In all your ways acknowledge Him, and He shall direct your paths. (Proverbs 3:6).

Introduction

W elcome to JavaScript: A Beginners Guide, Fourth Edition ! Years ago, I was surfing the Web and noticed that people were publishing pages about themselves and calling them homepages. After viewing a number of these, I decided to create a homepage myself. I had no idea where to begin but, through trial and error, I figured out how to code HTML and publish my documents on a Web server. Over time, I saw some interesting effects used on other homepages (like alert messages that popped up out of nowhere or images that would magically change when I moved my mouse over them). I was curious and just had to know what was being done to create those effects. Were these page creators using HTML tags I did not know about?

Eventually, one site revealed what they were using to create those effects: JavaScript. I went in search of information on it, and came across a few tutorials and scripts on the Web. Since I had programmed in other languages (such as a relatively obscure language called Ada), I was able to catch on to JavaScript fairly quickly by looking at these tutorials and scripts.