Dojo深度解析：权威指南

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"Dojo权威指南" Dojo 是一个强大的JavaScript库，它提供了丰富的功能，包括AJAX、动画、事件处理、DOM操作、模块化开发等，帮助开发者构建高效、可维护的Web应用程序。《Dojo权威指南》作为一本大师级的教程，深入探讨了Dojo框架的各个方面，是Dojo爱好者和专业人士不可或缺的参考资料。本书可能涵盖了以下主要知识点： 1. **Dojo基础**：介绍Dojo的核心概念，如dojo.js的加载机制，如何在项目中引入Dojo库，以及Dojo的模块系统（dojo.require, dojo.provide等）。 2. **dojo.dom**：讲解DOM操作API，包括获取元素、创建元素、修改元素属性、添加和删除元素等。 3. **dojo.event**：介绍事件处理机制，包括事件绑定、事件冒泡、事件阻止等，以及Dojo的事件对象和事件处理函数。 4. **dojo.fx**：讲解动画效果的实现，如淡入淡出、滑动、旋转等，以及如何组合多个动画效果。 5. **dojo.data**：介绍数据存储和检索机制，如ItemFileReadStore和ItemFileWriteStore，用于与服务器数据交互。 6. **dojo.ajax**：深入讨论AJAX技术，包括dojo.xhrGet, dojo.xhrPost等方法，以及XMLHttpRequest的使用和异步处理。 7. **dojo.declare**：解释类和面向对象编程，如何使用dojo.declare定义类，实现继承和多态。 8. **dijit**：Dijit是Dojo的UI组件库，涵盖各种用户界面元素，如按钮、表单、对话框等，以及如何自定义和主题化dijit。 9. **dojox**：dojox是Dojo的扩展库，包含许多高级和实验性的功能，如图表、地理空间、多媒体支持等。 10. **模块化开发**：讲解Dojo的AMD（Asynchronous Module Definition）模块化开发方式，如何通过dojo/require和define实现模块化代码组织。 11. **国际化和本地化**：介绍Dojo如何处理多语言和文化差异，使用dojo/i18n和dojo/text等模块。 12. **性能优化**：讨论如何利用Dojo工具链（如build系统）进行代码压缩、合并，以提高页面加载速度和性能。 13. **Dojo工具和开发环境**：介绍Dojo的构建工具、调试器和其他辅助开发工具的使用。此外，书中可能还会提供实践案例和最佳实践，帮助读者理解并应用Dojo到实际项目中。O'Reilly出版社还提供了其他相关资源，如《Adding Ajax》和《JavaScript: The Definitive Guide》，这些书籍可以作为JavaScript和AJAX技术的补充学习材料。访问oreilly.com，你可以找到更多关于Dojo和其他开放技术的新闻、事件、文章、博客、样本章节和代码示例。同时，O'Reilly的Safari Bookshelf在线参考图书馆提供超过1000本书的搜索和订阅服务，对于程序员和IT专业人士来说，这是一个宝贵的在线学习平台。

xiv

Foreword

These kinds of accomplishments aren’t the work of one person, or even a small team.

The number of people who have contributed to Dojo’s evolution, believed in the

project, and worked together to deliver a better Web are too numerous to mention.

We copied what we thought were the best bits of the structures of other projects, and

the result has been a level playing field and rules that are fair to users, contributors,

and sponsors alike. Dojo is proof that open source isn’t just a handy distribution

model for closed systems, but that collaborative, open projects can thrive when they

adopt policies that let users trust a project and when those inside the project finds

ways to trust each other. For all of the technical achievements embodied in the tool-

kit, I’m most proud that we’ve done it in the open, with anyone who will join us, and

done it honestly. We set out to build a project that values all kinds of contributions,

not just code. A project that would help change the tone of open source develop-

ment to encourage collegial, civil discourse. A project dedicated to building with the

community and not to treat users as “them.” “They” are “us” and this book makes

plain the open philosophy under which the toolkit was built, and by which we

encourage all those reading it to help us evolve it for the future.

By the time I met Matthew Russell face-to-face, this book was nearly “in the can.”

Open source is funny like that—you can work for years with someone, yet the pieces

picked up over mailing lists and IRC don’t fall into place until you’re talking about

the mundane and thrilling over a good local ale (or, in a pinch, Guinness). It wasn’t

until Matthew and I were comparing notes in an old, small, quiet pub in San Fran-

cisco’s North Beach district that it clicked: his technical depth, curiosity, and ability

to meet you on your level are the hallmarks of a great teacher. As I reviewed the draft

chapters in turn, I found myself constantly deleting what I’d just written by way of

critique as Matthew laid out the concepts in just the right order. Matthew’s illumina-

tions make Dojo approachable, friendly, and productive. The constant delight of dis-

covery that glows so brightly when you talk to Matthew in person are a true gift to

this volume.

It has been like this for me for nearly four years now as I’ve had the chance to put

faces to the IRC handles and forum posts. In open source, each person enters your

world as a technical problem to be solved, a bug to be fixed, or a feature to be con-

sidered. Only later is the full measure of the people you’re working with made plain,

and it’s nearly always a breathtaking revelation. The kindness, selfless effort, and tal-

ent that are freely given are humbling particularly in light of the personal sacrifices

that each person makes to be a part of the project. Matthew’s book is a credit to the

amazing team I’ve had the honor to work with.

I can’t say that I recommend dropping out of college to work on things that no one

will pay you for, but if that fire starts in your brain, don’t ignore it. If it leads you to

people only half as wonderful as those I’ve met and now count among my friends, it

will be worth every sleepless night.

—Alex Russell

Cofounder, Dojo Toolkit, and Dojo Foundation

President

xvi

Preface

Dojo packs the standard JavaScript library you’ve always wanted, the collection of

drop-in replacements for the customized HTML controls and CSS layout hacks

you’ve implemented again and again, and the build tools and unit tests that would

have been so handy when it came time for migrating to production. Dojo isn’t just a

JavaScript toolkit, Dojo is the JavaScript toolkit—and right now is a great time to

learn how to use it to make your life easier and the experience of your end users

everything that it possibly can be. Dojo is revolutionizing web development, and

gaining momentum fast.

Whatever web development project may be on your horizon, rest assured that Dojo

can help you realize it quickly and with minimal boilerplate so that you’re left with

the cleanest, most maintainable implementation possible. My sincere hope is that

this book relates Dojo’s story so effectively that you’ll spend minimal time scram-

bling around for answers and be able to fully concentrate on engaging the challeng-

ing (and far more interesting) problems that you’ve set out to solve.

Why Dojo?

Undoubtedly, there is a swatch of JavaScript toolkits available today, so you might

already be wondering what Dojo provides that you can’t get somewhere else. Keep-

ing in mind that the very nature of a toolkit or library being built upon a completely

interpreted language makes it theoretically possible for any other toolkit to do the

very same things, it’s not so much what can Dojo do that other can’t do; rather, it’s

more about the effectiveness of getting work done along with the community, philos-

ophy, and licensing aspects that surround it.

You might think of it like this: it’s theoretically possible to build a house using only a

hammer, a shovel, a saw, and a lot of nails—but at what expense? Clearly, some

heavy machinery and some carpenters to support you along the way would be a tre-

mendous boon. The situation with Dojo is quite similar. The following list attempts

to highlight (in no particular order) some of the places where Dojo really shines and

differentiates itself:

Community

Although it could be considered a nontechnical issue, Dojo’s open community is

one of its top strengths. The Dojo Foundation, a nonprofit organization set up for

the purpose of providing a vendor-neutral guardian of intellectual property, backs

the toolkit (and other interesting projects such as Cometd,

DWR,

†

and Open-

Record

‡

), and is sponsored and supported by IBM, AOL, Sun, OpenLaszlo,

* See http://www.cometd.com or http://www.cometdaily.com or a great coverage on Comet.

† See http://getahead.org/dwr for more on Direct Web Remoting.

‡ See http://www.openrecord.org for more on OpenRecord.

Preface

xvii

Nexaweb, SitePen, BEA, Renkoo, and a slew of the greatest DHTML hackers in

the world. If that doesn’t tell you that it has good friends backing it, then what

possibly could?

As a liberally licensed open source project with extremely low barriers to entry,

your voice will be heard if you want it to be heard. If you pop into the IRC chat

room #dojo on freenode.net and start talking, there’s virtually no chance that

you won’t be heard by a committer or significant contributor to the project.

Additionally, weekly IRC meetings are currently held on #dojo-meeting each

Wednesday from 3 to 6 P.M. (PST), and you’re more than welcome to pop in

and eavesdrop or participate in the official meetings where both strategic and

tactical issues are routinely discussed.

Knowing there’s transparency in how Dojo is steered strategically and devel-

oped tactically is very compelling. As other JavaScript toolkits and libraries

become increasingly commoditized, the Dojo community really stands out as

different. The organizations and individuals who make up the team of commit-

ters (not to mention the thousands of individual developers out there building

real web sites and applications) all give Dojo a particular character and ground-

ing for success.

Liberal (and clean) licensing

Dojo is open source software that is liberally licensed under the terms of either

the modified Berkeley Software Distribution (BSD) license or the Academic Free

License (AFL) version 2.1. Except as noted in a few per-module license files, you

get to choose the license you want to adopt for your specific work. All external

contributions are required to be compatible with the BSD or AFL licenses, and

all contributors must sign a Contributor License Agreement (CLA) that ensures

the Dojo Foundation has clear title to all contributions—thereby protecting all

users of the toolkit from intellectual licensing conundrums. The benefit of clean

licensing is markedly not the case with several other popular JavaScript toolkits

(that shall be left unnamed).

Depth and breadth

While some toolkits tackle specific pieces of a problem space, Dojo provides an

end-to-end solution for development in the browser. Everything from standard

library utilities to turnkey widgets to build tools and a testing framework—it’s

all in there, so you seldom have to look elsewhere. But don’t let the breadth fool

you into thinking that there is code bloat, because the build tools allow you to

produce custom versions of the toolkit that can be as streamlined as your appli-

cation permits.

While it is often the case that breadth hampers depth, it’s not what happens

with Dojo at all. Even inside of Base, the tiny kernel that provides the founda-

tion for the rest of the toolkit, you have more functionality than you can shake a

stick at—facilities for universally querying the DOM via CSS3 selectors, AJAX

xviii

Preface

utilities, event normalization amongst various browsers—and then some. That

doesn’t even begin to touch of the rich library of application, form, and layout

widgets, or the build tools.

Although the breadth and depth of Dojo produces a lot of complexity, the infra-

structure is painstakingly reviewed on a continual basis by the some of the best

web hackers in the world for high quality coding standards, consistent naming

conventions, performance, maintainability, and overall ease of use for the appli-

cation developer. Rest assured that you will be able to create a great user experi-

ence with Dojo.

Portability

While the JavaScript language is dynamic, powerful, and extremely expressive,

there are still myriad issues that come up routinely that amount to fairly mun-

dane engineering efforts. It’s quite instructive to go through the motions that

solve a central algorithmic problem or engineering conundrum, but at the end of

the day, any code that you develop is code that you have to maintain, update,

debug, and document.

As if those aren’t enough good reasons, the motivation for having a JavaScript

standard library may be especially compelling given the existing state of compat-

ibility amongst browsers for various feature sets. While attempting to develop a

feature that works uniformly across a set of modern browsers may not always be

rocket science, it can be painfully tedious work that can demoralize even the

most seasoned professionals.

The bottom line is that it’s almost a certainty that as an application developer,

you aren’t going to be receiving any return on investment (or having very much

fun) by jumping through all of those hoops. Instead, pick up production quality

code that a community of other developers has developed, debugged, and

tested—and then consider contributing back. Hopefully, that “giving back” part

will come naturally enough once you’ve saved enough time and money by way

of community-supported, open source software.

Pragmatic philosophy

Dojo embraces JavaScript for what it is instead of treating it like it’s something

that’s broken and thereby trying to create a brittle, artificial layer on top of it

that almost redefines it. While Dojo exposes tremendous functionality that pro-

tects you from the bare metal of the browser and does many things like normal-

ize browser events behind the scenes so that you don’t even have to think twice

about them, it never attempts to reinvent JavaScript. For example, you won’t

find Dojo-specific functions for operations like deleting DOM nodes or walking

the DOM tree because operations like

childNodes, firstChild, lastChild, and

removeChild work just fine across all browsers. However, whenever there are

known inconsistencies, Dojo steps in to provide you with the tools you need to

write portable code.

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