JavaScript复兴：宽带与Ajax技术推动的革新

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JavaScript，诞生于1995年，起源于 Netscape Navigator 2 中嵌入的客户端脚本，经历了显著的兴衰起伏。早期浏览器间的兼容性问题曾困扰开发者，但随着 Internet Explorer 6 的稳定性和W3C DOM Level 2标准的引入，使得开发者能够依赖兼容性解决方案，即使微软并未完全遵循这一标准，其他浏览器如Mozilla、Safari和Opera则选择遵循W3C标准。如今，JavaScript和Dynamic HTML重获关注的两大因素是宽带网络的普及和XMLHttpRequest对象的广泛应用。随着互联网速度的提升，以前在拨号上网时可能导致页面加载缓慢的大量脚本现在对用户来说不再是问题。XMLHttpRequest（XHR）使得浏览器与服务器可以在后台进行通信，允许脚本请求并更新页面的部分内容，这比一次性下载大量数据或通过提交表单等待新页面加载更为高效且视觉上更流畅。这种技术催生了所谓的"异步JavaScript和XML"(Ajax)应用，它利用了这种实时数据更新的能力。相关资源包括《JavaScript & DHTML Cookbook》、《CSS Cookbook》、《CSS: The Definitive Guide》、《Dynamic HTML: The Definitive Reference》、《HTML & XHTML: The Definitive Guide》以及《JavaScript: The Definitive Guide》等书籍，这些都提供了深入学习和实践JavaScript的宝贵资源。O'Reilly网站提供了一个全面的图书目录，包括新闻、活动、文章、博客、样本章节和代码示例，对于开发者来说是不可或缺的资源。此外，O'Reilly还举办各类会议，汇集创新者分享前沿技术和知识，帮助开发者掌握最新的工具和系统，将创新者的智慧转化为实用技能。在线参考库Safari Bookshelf为程序员和IT专业人士提供了超过1000本书的搜索服务，订阅者可以获取即时的答案和资源。 JavaScript的复兴得益于宽带网络的加速、跨平台的XMLHttpRequest技术以及丰富的学习资源和社区支持。它现已成为构建高效、响应式的Web应用的重要工具，推动了现代Web开发的革新。

About the Recipes

copyrights to worry about, as long as you don’t offer these recipes to others as

part of a collection of scripts. Of course, if you wish to acknowledge this book in

your source code comments, that would be great!

• You may be an experienced web developer who has probed gingerly, if at all,

into client-side scripting. The horror stories of yore about browser incompatibili-

ties have kept your focus entirely on server-side programming. But now that so

many mainstream sites are using client-side scripting to improve the user experi-

ence, you are ready to take another look at what is out there.

• At the far end of the spectrum, you may be an experienced client-side DHTML

developer in search of new ideas and techniques. For instance, you may have

developed exclusively for the Internet Explorer browser on the Windows plat-

form, but you wish to gravitate toward standards-compatible syntax for future

coding.

Virtually every reader will find that some recipes in this book are too simple and oth-

ers are too complex for their experience level. I hope the more difficult ones chal-

lenge you to learn more and improve your skills. Even if you think you know it all,

be sure to check the discussions of the easier recipes for tips and insights that may be

new to you.

About the Recipes

It’s helpful for a reader to know upfront what biases an author has on the book’s

subject. To carry the cookbook metaphor too far, just as a culinary chef has identifi-

able procedures and seasonings, so do I format my code in a particular way and

employ programming styles that I have adopted and updated over the years.

More important than scripting style, however, are the implementation threads that

weave their way throughout the code examples. Because these examples may serve as

models for your own development, they are written for maximum clarity to make it

easy (I hope) for you to follow the execution logic. Names assigned to variables,

functions, objects, and the like are meant to convey their purpose within the context

of the example. One of the goals of coding is that the operation of a program should

be self-evident to someone else reading the code, even if that “someone else” is the

programmer who revisits the code six months later to fix a bug or add a feature.

There’s no sense in being cryptically clever if no one can understand what you mean

by assigning some value to a variable named

This book unabashedly favors the W3C DOM way of addressing document objects.

You can use this format to reference element objects in browsers starting with

Microsoft Internet Explorer 5 and the other mainstream browsers addressed in this

edition (Mozilla-based browsers, Safari, and Opera 7 or later), which means that the

vast majority of browsers in use today support this standard. Where IE (including

xvi

Preface

IE 7) does not support the standard (as in handling events), all recipes here include

efficient cross-browser implementations. You won’t find too much in the way of IE-

only solutions, especially if they would cover only the Windows version of IE.

The long period of browser stability we have enjoyed since the first edition means

that visitors to public sites almost never use what are now antique browsers—IE

prior to 5.5 and Netscape Navigator 4 or earlier. All recipes are optimized for the

current browsers, but they also try to prevent hassles for anyone driving by in her

steam-powered browser.

One credo dominates the recipes throughout this book: scripting must add value to

static content on the page. Don’t look to this book for scripts that cycle background

colors to nauseate visitors or make elements bounce around the page while singing

“Happy Birthday.” You may be able to figure out how to do those horrible things

from what you learn in this book, but that’s your business. The examples here, while

perhaps conservative, are intended to solve real-world problems that scripters and

developers face in professional-quality applications.

The scripting techniques and syntax you see throughout this book are designed for

maximum forward compatibility. It’s difficult to predict the future of any technol-

ogy, but the W3C DOM and ECMAScript standards, as implemented in today’s lat-

est browsers, are the most stable platforms on which to build client-side applications

since client-side scripting began. With a bit of code added here and there to degrade

gracefully in older browsers, your applications should be running fine well into the

future.

What’s in This Book

The first four chapters focus on fundamental JavaScript topics. In Chapter 1, Strings,

you will see the difference between a string value and a string object. Regular expres-

sions play a big role in string parsing for these recipes. You will also see a reusable

library for reading and writing string data to cookies. Chapter 2, Numbers and Dates,

includes recipes for handling number formatting and conversions, as well as date cal-

culations that get used in later recipes. Perhaps the most important core JavaScript

language chapter is Chapter 3, Arrays and Objects. Recipes in this chapter provide

the keys to one- and multidimensional array creation, array sorting, object creation,

hash table simulation, and exploration of the prototype inheritance powers of

objects. You also see how creating custom objects for your libraries can reduce

potential naming conflicts as projects grow. Chapter 4, Variables, Functions, and

Flow Control, includes a recipe for improving overall script performance.

Chapter 5 through Chapter 8 provide solutions for problems that apply to almost all

scriptable browsers. In Chapter 5, Browser Feature Detection, you will learn how to

free yourself of the dreaded “browser sniffing” habit and use forward-compatible

techniques for determining whether the browser is capable of running a block of

Browser Platforms

xvii

script statements. If multiple windows are your nemesis, then Chapter 6, Managing

Browser Windows, provides plenty of ideas to handle communication between win-

dows. A few recipes present suggestions for modal windows (or facsimiles thereof).

Not everyone is a frame lover, but Chapter 7, Managing Multiple Frames, may be of

interest to all, especially if you don’t want your site being “framed” by another site.

Intelligent forms—one of the driving forces behind the creation of client-side script-

ing—are the subject of Chapter 8, Dynamic Forms. Updated to modern techniques,

recipes include form validation (with or without regular expressions) and some cool

but subtle techniques found on some of the most popular web sites on the Internet.

Interactivity with the user is driven by event processing, and Chapter 9, Managing

Events, covers the most common event processing tasks you’ll encounter with

DHTML scripting. Events (and one of the libraries shown in Chapter 9) ripple

through most of the remaining chapters’ recipes. That includes many recipes in

Chapter 10, Page Navigation Techniques, where you’ll see how to implement a vari-

ety of menuing designs and pass data from one page to the next. Chapter 11, Manag-

ing Style Sheets, provides recipes for both basic and advanced style sheet techniques

as they apply to dynamic content, including how to load a browser- or operating sys-

tem-specific stylesheet into the page. Style sheets play a big role in Chapter 12, Visual

Effects for Stationary Content, where recipes abound for image rollovers and user-

controlled font sizes, to name a couple.

Chapter 13, Positioning HTML Elements, addresses numerous challenges in keeping

positioned elements under tight rein. A positioning library recipe is used extensively

throughout the rest of the book, including more recipes in this chapter for animating

elements, scrolling content, and creating a draggable element. In Chapter 14, Creat-

ing Dynamic Content, the W3C DOM and

XMLHttpRequest object get good workouts

with recipes for tasks such as embedding JavaScript and XML data within a docu-

ment, transforming data into renderable HTML content, and sorting HTML tables

instantly on the client. Additional dynamic content recipes come in Chapter 15,

Dynamic Content Applications, where more complex recipes show you how to use

DHTML for a slide show, a user-editable document, and a pop-up calendar date

picker, among others.

Browser Platforms

Freed from having to worry much about compatibility with very old browsers, the

goal of each recipe’s design in this edition is to work in the following browsers:

• Microsoft Internet Explorer 6 or later

• Mozilla 1.7.5 (Firefox 1.0, Netscape 8.0, Camino 1.0) or later

• Apple Safari 1.2 or later (including the Windows version)

• Opera 7 or later

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