About the Technical Reviewer After getting hooked on the Web in 1996 and spending several years pushing pixels and bits for the likes of IBM and Konica Minolta, AARON GUSTAFSON founded his own web consultancy: Easy! Designs. Aaron is a member of the Web Standards Project (WaSP) and the Guild of Accessible Web Designers (GAWDS). He also serves as a technical edi- tor for A List Apart, is a contributing writer for Digital Web Magazine and MSDN, and has built a small library of writing and editing credits in the print world, including con- tributions to AdvancED DOM Scripting (friends of ED, 2007), Accelerated DOM Script- ing with Ajax, APIs, and Libraries (Apress, 2007), and Web Design in a Nutshell, Third Edition (O’Reilly, 2006). Aaron has graced the stage at numerous conferences, including An Event Apart, COMDEX, South by Southwest, the Ajax Experience, and Web Direc- tions, and he is frequently called on to provide web standards training in both the pub- lic and private sectors. He blogs at http://easy-reader.net. xv Acknowledgments Anumber of forces conspired to help me finish this book, despite my best efforts not to. Aaron Gustafson was a great help as technical editor and gave thoughtful code cri- tiques. The patient, stoic folks at Apress gave me constructive encouragement through- out the slow, arduous process. Christophe Porteneuve, having written a book on the same subject, gave me tips on several occasions. I am also grateful to Sam Stephenson, both for creating Prototype and for inviting me to be a part of Prototype Core. Other team members gave critical moral support: Thomas Fuchs, Tobie Langel, Mislav Marohnic, and Justin Palmer. Objects, as well as people, were instrumental in the completion of this book: a MacBook Pro, TextMate, Parallels Desktop, and sugar-free Red Bull. I thank them for their support. xvii Introduction Iwrote this book for people who have some experience with JavaScript and no experi- ence with Prototype. I mean for “experience with JavaScript” to cast a wide net: you may love JavaScript, or hate it, or love the language but hate browser scripting, or love both, or hate both. Because the book assumes some JavaScript experience, it does not cover the most basic parts of the JavaScript language itself, nor does it cover the DOM. There are many books that can get you started on that path, but the best free resource is Quirks Mode ( www.quirksmode.org), the authoritative and exhaustive reference created by Peter-Paul Koch. This book is also meant to appeal to those who have some experience with Proto- type but don’t consider themselves experts. Many have worked with Prototype indirectly through Ruby on Rails or a similar framework. Many have used a third-party script that depended on Prototype, but treated the code as a black box. In the first chapter of the book, we’ll look at some aspects of the JavaScript language that novice users may not know about. Feel free to spend as much time on Chapter 1 as you need, since it’s crucial that you understand these concepts if you want to use Proto- type effectively. The screenshots in this book show Firefox running on Windows XP, but the code examples are designed to work in all major browsers and on all major platforms. Proto- type boasts official support for Firefox (versions 1.5 and above), Internet Explorer (6 and above), Safari (2 and above), and Opera (9.2 and above). I welcome your feedback, observations, and ridicule. I can be reached at book@andrewdupont.net. xix Prototype PART 1 What You Should Know About Prototype, JavaScript, and the DOM Before jumping into the deep end, you should learn about where Prototype comes from—its purpose, origin, and philosophy. We’ll also discuss what differentiates Proto- type from other libraries. First, though, we need to make sure we’re on the same page. This book assumes a basic familiarity with JavaScript and the DOM, but that’s a vague prerequisite, and JavaScript is a language both broad and deep. In case you need a refresher, here’s a crash course in topics that will be built upon in the chapters to follow. About JavaScript George Orwell once wrote that writing JavaScript “is a horrible, exhausting struggle, like a long bout of some painful illness. One would never undertake such a thing if one were not dr iven on by some demon whom one can neither resist nor understand.” OK, that’s a lie. He actually said that about writing books.K eep in mind, though, that JavaScript had not yet been created in Orwell’s time, and that a modern-day Orwell might have eschewed prose in favor of progr amming , a far higher artistic pursuit. I feel this way about Jav aScript, at the very least. It’s a brilliant language with very public flaws. It was created hastily and standardized prematurely. The JavaScript envi- ronments within browsers vary wildly in spec compliance, language features, and speed. It’s a language whose ideals are compromised by the imperfect state of today’s Web. We’ll talk about ways to mitigate these flaws. But first let’s look at some of the things that make JavaScript brilliant. 3 CHAPTER 1 Everything Is an Object The sooner you embrace this concept, the more quickly you’ll understand Prototype: everything in JavaScript is an object. This has several different meanings and several different implications, which are outlined in the following subsections. All Data Types Have Instance Methods Like other languages that embrace object orientation, every object can have instance methods. This allows for flexible syntax and makes code easier to read. ["foo", "bar", "baz"].join(' '); //=> "foo bar baz" "foo bar baz".split(' '); //-> ["foo", "bar", "baz"] It also ensures that functions don’t clutter up the global namespace. What’s the use of a generic join function, for instance, if it works only on arrays? Or a generic split that works only on strings? All Data Types Inherit from Object JavaScript boasts half a dozen native data types: Object, String, Array, RegExp (for regular expressions), Boolean (true or false), and Date. I place Object first because it’s the root data type. When I say that everything in JavaScript is an object, I also mean that everything in JavaScript is an Object. Confused? Let me explain. Object can be thought of as a blank data type, the empty canvas that all other types start with. There is nothing Object does that another type can’t do, but then that’s the point: Objects can bend to your will. But back to the main point: Everything in JavaScript is an Object. We can verify this with the instanceof operator on some core JavaScript data types: Array instanceof Object; //-> true RegExp instanceof Object; //-> true Date instanceof Object; //-> true String instanceof Object; //-> true Function instanceof Object; //-> true CHAPTER 1 ■ WHAT YOU SHOULD KNOW ABOUT PROTOTYPE, JAVASCRIPT, AND THE DOM4 . 1996 and spending several years pushing pixels and bits for the likes of IBM and Konica Minolta, AARON GUSTAFSON founded his own web consultancy: Easy! Designs. Aaron is a member of the Web Standards. both for creating Prototype and for inviting me to be a part of Prototype Core. Other team members gave critical moral support: Thomas Fuchs, Tobie Langel, Mislav Marohnic, and Justin Palmer. Objects,. browsers and on all major platforms. Proto- type boasts official support for Firefox (versions 1.5 and above), Internet Explorer (6 and above), Safari (2 and above), and Opera (9.2 and above). I