全面掌握ES6：《ECMAScript 6权威指南》开发者详解

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《理解ECMAScript 6：JavaScript开发者指南》是一本由Nicholas C. Zakas编写的权威书籍，专为前端开发和Web开发人员设计。本书深入讲解了ECMAScript 6（ES6）的新特性和语言改进，这是JavaScript语言的一个重要里程碑，旨在提升代码的可读性、简洁性和性能。作者在书中详细阐述了诸如箭头函数、模板字符串、解构赋值、类和模块系统、Promise与async/await等核心概念。 ES6引入了一系列旨在简化开发过程的语法特性。例如，箭头函数消除了传统函数的`function`关键字，使得代码更简洁；模板字符串使用反引号(`)来创建包含变量和表达式的字符串，提供了更好的字符串插值功能。此外，解构赋值允许开发者更方便地从数组或对象中提取值赋给变量，提高了代码的可读性和效率。类是面向对象编程的重要组成部分，在ES6中被重新设计，支持构造函数、继承和实例方法，这使得JavaScript的面向对象特性更加直观和强大。模块系统则解决了JavaScript长期以来的模块化问题，通过`import`和`export`语句，开发人员可以更好地组织和复用代码，提高代码的可维护性。 Promise和async/await是处理异步操作的关键工具，它们使得处理回调地狱变得更加容易，提升了代码的可读性和错误处理能力。书中还涉及其他新特性，如默认参数、剩余参数、可选链操作符等，这些都显著提升了JavaScript的灵活性和现代性。《Understanding ECMAScript 6》是一本不可或缺的参考书，无论是对于希望深入理解ES6的开发者，还是希望提升自己的JavaScript技能的工程师，都是学习和实践ES6的最佳资源。阅读这本书将帮助读者更好地适应现代JavaScript开发环境，提升代码质量和项目管理能力。

xiv Contents in Detail

Global Promise Rejection Handling .................................... 224

Node.js Rejection Handling ................................... 225

Browser Rejection Handling ................................... 227

Chaining Promises ................................................ 228

Catching Errors............................................ 229

Returning Values in Promise Chains.............................. 230

Returning Promises in Promise Chains ............................ 231

Responding to Multiple Promises ...................................... 233

The Promise.all() Method ..................................... 234

The Promise.race() Method.................................... 235

Inheriting from Promises ............................................ 236

Promise-Based Asynchronous Task Running ............................... 237

Summary ...................................................... 241

PROXIES AND THE REFLECTION API 243

The Array Problem ................................................ 244

Introducing Proxies and Reflection ..................................... 244

Creating a Simple Proxy ............................................ 245

Validating Properties Using the set Trap ................................. 246

Object Shape Validation Using the get Trap .............................. 247

Hiding Property Existence Using the has Trap ............................. 249

Preventing Property Deletion with the deleteProperty Trap ..................... 250

Prototype Proxy Traps .............................................. 252

How Prototype Proxy Traps Work ............................... 252

Why Two Sets of Methods? ................................... 254

Object Extensibility Traps ........................................... 255

Two Basic Examples ........................................ 255

Duplicate Extensibility Methods................................. 256

Property Descriptor Traps ........................................... 257

Blocking Object.defineProperty()................................ 258

Descriptor Object Restrictions .................................. 259

Duplicate Descriptor Methods .................................. 260

The ownKeys Trap ................................................ 261

Function Proxies with the apply and construct Traps ......................... 262

Validating Function Parameters................................. 264

Calling Constructors Without new ............................... 265

Overriding Abstract Base Class Constructors ....................... 266

Callable Class Constructors ................................... 267

Revocable Proxies ................................................ 268

Solving the Array Problem........................................... 269

Detecting Array Indexes...................................... 270

Increasing length When Adding New Elements...................... 270

Deleting Elements When Reducing length.......................... 272

Implementing the MyArray Class................................ 273

Using a Proxy as a Prototype......................................... 275

Using the get Trap on a Prototype ............................... 276

Using the set Trap on a Prototype ............................... 277

Using the has Trap on a Prototype............................... 278

Proxies as Prototypes on Classes................................ 279

Summary ...................................................... 282

Contents in Detail xv

ENCAPSULATING CODE WITH MODULES 283

What Are Modules? .............................................. 283

Basic Exporting .................................................. 284

Basic Importing .................................................. 285

Importing a Single Binding.................................... 286

Importing Multiple Bindings ................................... 286

Importing an Entire Module ................................... 286

A Subtle Quirk of Imported Bindings ............................. 288

Renaming Exports and Imports........................................ 288

Default Values in Modules........................................... 289

Exporting Default Values ..................................... 289

Importing Default Values ..................................... 290

Re-exporting a Binding ............................................. 291

Importing Without Bindings .......................................... 292

Loading Modules ................................................. 293

Using Modules in Web Browsers ............................... 293

Browser Module Specifier Resolution ............................. 297

Summary ...................................................... 298

MINOR CHANGES IN ECMASCRIPT 6 299

Working with Integers ............................................. 299

Identifying Integers ......................................... 300

Safe Integers ............................................. 300

New Math Methods ............................................... 301

Unicode Identifiers ................................................ 302

Formalizing the __proto__ Property .................................... 303

UNDERSTANDING ECMASCRIPT 7 (2016) 305

The Exponentiation Operator......................................... 306

Order of Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

Operand Restriction ........................................ 306

The Array.prototype.includes() Method .................................. 307

How to Use Array.prototype.includes()............................ 307

Value Comparison ......................................... 308

A Change to Function-Scoped Strict Mode ............................... 308

INDEX 311

xviii Foreword

upcoming ECMAScript 6 (ES6) speciﬁcation, codenamed Harmony, was far

from ﬁnished and seemed like a distant future. “Maybe in 10 years I’ll get to

write some ES6 code,” I thought.

There were some experimental “transpilers” like Google Traceur that

translated code from ES6 into ES5. Most of them were very limited or hard

to plug into an existing JavaScript build pipeline. But then a new transpiler

called 6to5 came along and changed everything. It was easy to install, inte-

grated well with the existing tools, and produced readable code. It spread

like wildﬁre. Now called Babel, 6to5 brought ES6 features to a mainstream

audience even before the speciﬁcation was ﬁnalized. In a matter of months,

ES6 was everywhere.

ES6 has divided the community for a number of reasons. As this book

goes to press, it is still not fully implemented in many major browsers.

Having a build step can be intimidating when you’re just learning the

language. Some libraries have documentation and examples in ES6, and

you might wonder if it is possible to use those libraries in ES5 at all. This

contributes to the confusion. Many people didn’t expect any new features

in the language because it had almost never changed before. Others anx-

iously awaited the new features’ arrival and used all of them together—in

some cases beyond what was necessary.

Just as I was becoming proﬁcient with JavaScript, I felt that somebody

pulled the rug from under my feet, and now I had to learn a new language.

I felt bad about this for a few months. Finally, on Christmas Eve, I started

reading a draft of this book. I couldn’t put it down. Next thing I knew, it

was 3 am, everybody at the party was asleep, and I understood ES6!

Nicholas is an incredibly gifted teacher. He conveys deep details in a

straightforward way so they don’t go over your head. Apart from this book,

he is also known for creating ESLint, a JavaScript code analyzer that has

been downloaded millions of times.

Nicholas knows JavaScript like very few people do. Don’t miss the

chance to soak up some of his knowledge. Read this book, and you, too,

will become conﬁdent in your understanding of ES6.

Dan Abramov

React core team member and creator of Redux

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