成为JavaScript忍者：进阶指南

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"Secrets of JavaScript ninja 是一本由John Resig和Bear Bibeault合著的书籍，由Manning出版社出版。这本书旨在帮助读者提升JavaScript技能，从初级水平过渡到高级专家级别，成为JavaScript编程的高手。" 在《Secrets of the JavaScript Ninja》一书中，作者深入探讨了JavaScript的核心概念和高级特性，包括但不限于以下知识点： 1. **原型和原型链**：讲解了JavaScript中的对象是如何通过原型链进行继承的，以及如何利用原型进行对象扩展和复用。 2. **闭包**：详述了闭包的工作原理和应用，包括其在内存管理、数据封装和模块化中的角色。 3. **函数**：讨论了函数作为一等公民的特性，函数表达式、立即执行函数（IIFE）以及函数的高级用法如高阶函数和函数组合。 4. **异步编程**：涵盖了回调函数、Promise、async/await等处理异步操作的方法，以及事件循环和回调队列的工作机制。 5. **作用域和块级作用域**：解释了全局作用域、局部作用域以及ES6引入的let和const变量声明带来的块级作用域。 6. **模块系统**：对比分析了CommonJS、AMD、SystemJS和ES6模块的差异，指导如何在不同环境下选择和使用模块化方案。 7. **DOM操作**：介绍了高效地操作和修改DOM元素的方法，包括选择器API、事件处理和动画效果的实现。 8. **性能优化**：讨论了如何通过代码优化、减少DOM操作和提升渲染效率来提高JavaScript应用的性能。 9. **错误处理**：讲述了如何有效地捕获和处理运行时错误，以及如何建立健壮的异常处理机制。 10. **调试技巧**：分享了各种JavaScript调试工具和方法，如浏览器开发者工具的使用，以及如何创建和利用断点进行问题排查。 11. **TypeScript与ES6+**：探讨了现代JavaScript（如ES6、ES7、ES8等版本）的新特性，以及如何结合TypeScript提升代码的类型安全性和可维护性。通过本书的学习，读者不仅能够掌握JavaScript的高级技术，还能了解到最佳实践和行业标准，从而在实际项目开发中更加得心应手。书中实例丰富，理论与实践相结合，适合有一定基础的JavaScript开发者进一步提升自己的技术水平。

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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