Dojo深度探索：权威指南

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"Dojo权威指南提供了全面的Dojo框架的深入解析，旨在帮助开发者高效地利用Dojo进行Ajax和JavaScript应用的开发。该指南与其他O'Reilly出版社的知名技术书籍，如《Ajax权威指南》、《CSS Cookbook》、《JavaScript权威指南》等一脉相承，提供高质量的技术资源。在O'Reilly的官方网站oreilly.com上，读者可以找到更多相关的新闻、事件、文章、博客、样本章节和代码示例，以及针对开放和新兴技术的开发者资源。此外，O'Reilly还举办各种会议，将创新者聚集在一起，推动技术的发展。对于专业人士，Safari Bookshelf在线参考图书馆是一个宝贵的资源，它允许用户搜索上千本书的内容并订阅获取最新资讯。" 本文将详细阐述Dojo框架的核心概念、功能及其在实际开发中的应用。 Dojo是一个开源JavaScript库，它为构建富互联网应用程序（Rich Internet Applications，RIA）提供了强大的工具集。Dojo的主要特点包括模块化系统（AMD，Asynchronous Module Definition）、DOM操作、动画效果、数据绑定、事件处理、AJAX通信以及丰富的UI组件。通过使用Dojo，开发者可以更轻松地实现页面动态更新、数据交互、性能优化等功能。 1. **模块化系统**：Dojo采用AMD规范，允许开发者异步加载和组织代码，提高网页加载速度，同时降低了代码间的耦合度。 2. **DOM操作**：Dojo提供了简便的DOM操作API，如dojo.query用于选择元素，dojo.place用于插入元素，使得DOM操作更加直观和高效。 3. **动画效果**：Dojo的dojox.fx模块包含了多种动画效果，如淡入淡出、滑动、旋转等，使开发者能够创建丰富的用户界面体验。 4. **数据绑定**：Dojo的数据绑定机制（如dojo.data和dijit.form）简化了模型与视图之间的同步，降低了维护复杂状态的难度。 5. **AJAX通信**：Dojo的dojo.xhr模块提供了对AJAX请求的支持，包括GET、POST以及其他HTTP方法，方便与服务器进行异步数据交换。 6. **UI组件**：Dojo的dijit模块包含了一系列预封装的UI组件，如按钮、表单、日历、树形视图等，它们具有良好的可定制性和可访问性。 7. **国际化和本地化**：Dojo支持多语言和区域设置，通过dojo/i18n模块，开发者可以轻松实现应用程序的国际化。 8. **工具和辅助库**：Dojo还提供了一些实用工具，如dojo/_base提供基础功能，dojo/json用于JSON处理，dojo/aspect用于面向切面编程等。通过阅读《Dojo权威指南》，开发者不仅可以掌握Dojo的基本使用，还能了解到高级特性和最佳实践，从而提升开发效率和应用质量。配合O'Reilly提供的其他相关技术资源，可以形成一个全方位的学习和参考资料体系。

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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