成为JavaScript忍者的关键秘密

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"Secrets of the javascript Ninja" 是一本由 John Resig 和 Bear Bibeault 合著的专业 JavaScript 技术书籍，由 Manning 出版社出版。这本书深入探讨了 JavaScript 的高级技术和最佳实践，旨在帮助读者提升在 JavaScript 领域的技能，成为一名真正的“JavaScript 忍者”。在这本指南中，作者们分享了关于 JavaScript 的诸多秘密，包括但不限于以下几个关键知识点： 1. **基础语法强化**：书中的内容涵盖了 JavaScript 的基本语法，如变量、数据类型、函数、对象和数组等。作者通过实例和深入解释，帮助读者巩固这些基础知识。 2. **原型和原型链**：JavaScript 的原型和原型链是其面向对象特性的重要组成部分。书中详细讲解了如何利用原型实现继承，以及如何理解和操作原型链。 3. **闭包和作用域**：闭包是 JavaScript 中一个强大的工具，允许函数访问和操作外部作用域的变量。书中会深入讨论闭包的工作原理，以及如何避免常见的作用域陷阱。 4. **异步编程**：JavaScript 以其事件驱动和非阻塞I/O特性而闻名。书中会介绍回调函数、Promise 和现代的 async/await 语法，帮助读者掌握处理异步操作的最佳实践。 5. **DOM操作与事件处理**：作为Web开发的核心，JavaScript 与DOM的交互至关重要。本书将指导读者如何高效地操作DOM节点，以及如何优雅地处理用户事件。 6. **性能优化**：书中还会讨论如何通过优化代码来提高JavaScript应用程序的性能，包括减少DOM操作、缓存策略和避免内存泄漏等技巧。 7. **模块化和打包工具**：随着JavaScript应用规模的扩大，模块化变得越来越重要。书中可能涵盖CommonJS、ES6模块，以及如何使用Webpack或Rollup等工具进行代码打包。 8. **错误处理和调试**：有效的错误处理和调试技巧是任何开发者必备的技能。书中会介绍如何使用try/catch语句，以及如何利用浏览器的开发者工具进行调试。 9. **最新特性**：由于JavaScript不断进化，书中可能包含ECMAScript的新特性，如箭头函数、模板字符串、解构赋值、async/await等，让读者紧跟语言的发展步伐。 10. **测试和持续集成**：为了确保代码的质量和稳定性，书中会涉及单元测试、集成测试以及如何设置自动化测试流程和持续集成系统。通过阅读《Secrets of the javascript Ninja》，读者不仅能提升对JavaScript核心概念的理解，还能学习到专业级的开发技巧，从而在实际项目中编写出更高效、更可靠的代码。

about this book

JavaScript is important. That wasn’t always so, but it’s true now.

Web applications are expected to give users a rich user interface experience, and

without JavaScript, you might as well just be showing pictures of kittens. More than

ever, web developers need to have a sound grasp of the language that brings life to

web applications.

And like orange juice and breakfast, JavaScript isn’t just for browsers anymore. The

language has knocked down the walls of the browser and is being used on the server

in engines such as Rhino and V8, and in frameworks like Node.js.

Although this book is primarily focused on JavaScript for web applications, the

fundamentals of the language presented in part 2 of this book are applicable across

the board.

With more and more developers using JavaScript, it’s now more important

than ever that they grasp its fundamentals, so that they can become true ninjas of

the language.

Audience

This is not your first JavaScript book. If you’re a complete novice to JavaScript, or you

only understand a handful of statements by searching the web for code snippets, this

is not the book for you. Yet.

This book is aimed at web developers who already have at least a basic grasp of

JavaScript. You should understand the basic structure of JavaScript statements and

how they work to create straightforward on-page scripts. You don’t need to be an

ABOUT THIS BOOK

xvi

advanced user of the language—that’s what this book is for—but you shouldn’t be a

rank novice.

You should also have a working knowledge of

HTML

and

CSS

. Again, nothing too

advanced, but you should know the basics of putting a web page together.

If you want some good prerequisite material, grab one of the popular books on

JavaScript and web development, and then tackle this one. We can recommend

JavaScript: The Definitive Guide by David Flanagan, JavaScript: The Good Parts by Douglas

Crockford, and Head First JavaScript by Michael Morrison.

Roadmap

This book is organized to take you from an apprentice to a ninja in four parts.

Part 1 introduces the topic and some tools we’ll need as we progress through the

rest of the book.

Part 2 focuses on JavaScript fundamentals: aspects of the language that you take

for granted but aren’t really sure how they work. This may be the most important part

of the book, and even if it’s all you read, you’ll come away with a much sounder under-

standing of JavaScript, the language.

In part 3, we dive into using the fundamentals that we learned in part 2 to solve

knotty problems that the browsers throw at us.

Part 4 wraps up the book with a look at advanced topics focusing on lessons

learned from the creation of advanced JavaScript libraries, such as jQuery.

Let’s take a brief look at what each chapter will cover.

Chapter 1 introduces us to the challenges that we face as writers of advanced web

applications. It presents some of the problems that the proliferation of browsers cre-

ates, and suggests best current practices that we should follow when developing our

applications, including testing and performance analysis.

Chapter 2 discusses testing, taking a look at the current state of testing and test

tools. It also introduces a small but powerful testing concept, the assert, which will be

used extensively throughout the remainder of the book to make sure that our code

does what we think it should be doing (or sometimes to prove that it doesn’t!).

Armed with these tools, chapter 3 begins our foray into the fundamentals of the

language, starting, perhaps to your surprise, with a thorough examination of the func-

tion as defined by JavaScript. Although you might have expected the object to be the

target of first focus, it’s a solid understanding of the function, and JavaScript as a func-

tional language, that begins our transformation from run-of-the-mill JavaScript coders

to JavaScript ninjas!

Not being done with functions quite yet, chapter 4 takes the fundamentals we

learned in chapter 3 and applies them to problems we face in creating our applica-

tions. We’ll explore recursion—not only for its own sake, but because we can learn a

lot more about functions through scrutinizing it—and we’ll learn how the functional

programming aspects of JavaScript can be applied to not only make our code elegant,

but also more robust and succinct. We’ll learn ways to deal with variable argument

ABOUT THIS BOOK

xvii

lists, and ways to overload functions in a language that doesn’t natively support the

object-oriented concept of method overloading.

One of the most important concepts you can take away from this book is the sub-

ject of chapter 5: closures. A key concept in functional programming, closures allow

us to exert fine-grained control over the scope of objects that we declare and create in

our programs. The control of these scopes is the key factor in writing code worthy of a

ninja. Even if you stop reading after this chapter (but we hope that you don’t), you’ll

be a far better JavaScript developer than when you started.

Objects are finally addressed in chapter 6, where we learn how patterns of objects

can be created through the

prototype

property of the function, and we’ll learn how

objects are tied to functions for their definitions—one of the many reasons we dis-

cussed functions first.

Chapter 7 focuses on the regular expression, an often-overlooked feature of

the language that can do the work of scores of lines of code when used correctly.

We’ll learn how to construct and use regular expressions and how to solve some

recurring problems elegantly, using regular expressions and the methods that work

with them.

Part 2 on language fundamentals closes out with chapter 8, in which we learn how

timers and intervals work in the single-threaded nature of JavaScript.

HTML5

promises

to bring us relief from the confines of the single thread with web workers, but most

browsers aren’t quite there yet, and virtually all of the existing JavaScript code

depends upon a good understanding of JavaScript’s single-threaded model.

Part 3 opens with chapter 9, in which we open the black box of JavaScript’s run-

time code evaluation. We’ll look at various ways to evaluate code on the fly, including

how to do so safely and in the scope of our choosing. Real-world examples, such as

JSON

evaluation, metalanguages (a.k.a. domain-specific languages), compression and

obfuscation, and even aspect-oriented programming, are discussed.

In chapter 10, we examine the controversial

with

statement, which is used to

shorten references within a scope. Whether you are a fan or detractor of

with

, it exists

in a lot of code in the wild, and you should understand it regardless of whether you

think it’s the bomb or an abomination.

Dealing with cross-browser issues is the subject of chapter 11. We examine the five

key development concerns with regard to these issues: browser differences, bugs and

bug fixes, external code and markup, missing features, and regressions. Strategies

such as feature simulation and object detection are discussed at length to help us deal

with these cross-browser challenges.

Handling element attributes, properties, and styles is the focus of chapter 12.

While the differences in how the various browsers handle these aspects of elements

are slowly converging over time, there still exists a number of knotty problems that

this chapter describes how to solve.

Part 3 concludes in chapter 13 with a thorough investigation of event handling

in the browsers and ways to create a unified subsystem that handles events in a

ABOUT THIS BOOK

xviii

browser-agnostic manner. This includes adding features not provided by the browsers,

such as custom events and event delegation.

In part 4 we pick up the pace and delve deeply into advanced topics taken from the

heart of JavaScript libraries such as jQuery. Chapter 14 discusses how

DOM

manipula-

tion

API

s can be constructed to manipulate the Document Object Model at runtime,

including the Gordian knot of injecting new elements into the

DOM

Finally, in chapter 15, we discuss how

CSS

selector engines are constructed and the

different ways in which they parse and evaluate selectors. Not for the faint of heart,

this chapter, but it’s a worthy final test of your ninja-hood.

Code conventions

All source code in listings or in the text is in a

fixed-width

font

this

to sepa-

rate it from ordinary text. Method and function names, properties,

XML

elements,

and attributes in the text are also presented in this same font.

In some cases, the original source code has been reformatted to fit on the pages.

In general, the original code was written with page-width limitations in mind, but

sometimes you may find a slight formatting difference between the code in the book

and that provided in the source download. In a few rare cases, where long lines could

not be reformatted without changing their meaning, the book listings contain line-

continuation markers.

Code annotations accompany many of the listings, highlighting important con-

cepts. In many cases, numbered bullets link to explanations that follow in the text.

Code downloads

Source code for all the working examples in this book (along with some extras that

never made it into the text) is available for download from the book’s web page at

www.manning.com/SecretsoftheJavaScriptNinja.

The code examples for this book are organized by chapter, with separate folders

for each chapter. The layout is ready to be served by a local web server, such as the

Apache

HTTP

Server. Simply unzip the downloaded code into a folder of your choice

and make that folder the document root of the application.

With a few exceptions, most of the examples don’t require the presence of a web

server at all and can be loaded directly into a browser for execution, if you so desire.

All examples were tested in a variety of modern browsers (as of mid-2012), includ-

ing Internet Explorer 9, Firefox, Safari, and Google Chrome.

Author online

The authors and Manning Publications invite you to the book’s forum, run by Man-

ning Publications, where you can make comments about the book, ask technical ques-

tions, and receive help from the authors and other users. To access and subscribe to

the forum, point your browser to www.manning.com/SecretsoftheJavaScriptNinja and

click the Author Online link. This page provides information on how to get on the

ABOUT THIS BOOK

xix

forum once you are registered, what kind of help is available, and the rules of conduct

in the forum.

Manning’s commitment to our readers is to provide a venue where a meaningful

dialogue between individual readers and between readers and the authors can take

place. It’s not a commitment to any specific amount of participation on the part of the

authors, whose contribution to the book’s forum remains voluntary (and unpaid). We

suggest you try asking the authors some challenging questions, lest their interest stray!

The Author Online forum and the archives of previous discussions will be accessi-

ble from the publisher’s website as long as the book is in print.

About the cover illustration

The figure on the cover of Secrets of the JavaScript Ninja is captioned “Noh Actor,

Samurai,” from a woodblock print by an unknown Japanese artist of the mid-nineteenth

century. Derived from the Japanese word for talent or skill, Noh is a form of classical

Japanese musical drama that has been performed since the 14th century. Many char-

acters are masked, with men playing male and female roles. The samurai, a hero fig-

ure in Japan for hundreds of years, was often featured in the performances, and in

this print the artist renders with great skill the beauty of the costume and the ferocity

of the samurai.

Samurai and ninjas were both warriors excelling in the Japanese art of war, known

for their bravery and cunning. Samurai were elite soldiers, well-educated men who

knew how to read and write as well as fight, and they were bound by a strict code of

honor called Bushido (The Way of the Warrior), which was passed down orally from

generation to generation, starting in the 10th century. Recruited from the aristocracy

and upper classes, analagous to European knights, samurai went into battle in large

formations, wearing elaborate armor and colorful dress meant to impress and intimi-

date. Ninjas were chosen for their martial arts skills rather than their social standing

or education. Dressed in black and with their faces covered, they were sent on mis-

sions alone or in small groups to attack the enemy with subterfuge and stealth, using

any tactics to assure success; their only code was one of secrecy.

The cover illustration is from a set of three Japanes prints owned for many years by

a Manning editor, and when we were looking for a ninja for the cover of this book, the

striking samurai print came to our attention and was selected for its intricate details,

vibrant colors, and vivid depiction of a ferocious warrior ready to strike—and win.

At a time when it is hard to tell one computer book from another, Manning cele-

brates the inventiveness and initiative of the computer business with book covers

based on two-hundred-year-old illustrations that depict the rich diversity of traditional

costumes from around the world, brought back to life by prints such as this one.

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