精通高性能JavaScript编程

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"高性能JavaScript编程（英文版）" 《高性能JavaScript》是Nicholas C. Zakas撰写的一本关于优化JavaScript代码性能的专业书籍。本书主要面向具有一定JavaScript基础的读者，旨在帮助他们提升JavaScript应用的运行效率。在JavaScript编程领域，性能优化是一项关键任务，尤其在现代Web应用程序中，用户对速度和响应性有着更高的要求。这本书深入探讨了如何通过各种技术和策略来提高JavaScript代码的性能，包括但不限于： 1. **内存管理**：讲解了JavaScript中的内存分配和垃圾回收机制，以及如何避免内存泄漏，减少不必要的对象创建和引用，以优化内存使用。 2. **DOM操作**：探讨了高效地操作DOM元素的方法，如批处理DOM操作、延迟执行和利用文档碎片等技术来减少DOM遍历和修改带来的性能影响。 3. **事件处理**：分析了事件模型和事件处理函数的性能优化，如何避免事件冒泡和事件委托，以及正确使用事件监听器。 4. **函数和作用域**：讨论了函数的内部工作原理，包括闭包和作用域链，以及如何利用它们来编写高性能代码，避免不必要的作用域查找。 5. **代码组织和模块化**：提出了模块化设计原则，如立即执行函数表达式(IIFE)和命名空间，以减少全局变量污染，提高代码可维护性和性能。 6. **JavaScript引擎优化**：解释了JavaScript引擎的编译过程，如V8引擎的即时编译（JIT），以及如何编写能被引擎优化的代码。 7. **异步编程**：介绍了回调函数、Promise和async/await等异步处理方法，以及如何避免回调地狱，优化异步流程控制。 8. **网络优化**：讲解了如何减少HTTP请求，利用缓存策略，以及优化资源加载顺序以提高页面加载速度。 9. **性能分析**：提到了性能测试工具和技巧，如何定位和修复性能瓶颈，以及持续监控和改进代码性能的重要性。 10. **最佳实践和陷阱**：列举了一些常见的性能反模式，并给出了相应的优化建议，帮助开发者避免常见的性能陷阱。通过学习《高性能JavaScript》，读者不仅可以理解JavaScript性能优化的核心概念，还能掌握实际应用中的优化技巧，从而开发出更快、更稳定且用户体验更好的JavaScript应用程序。此外，书中还包含了大量实例和实际案例，帮助读者更好地理解和应用这些知识。

How This Book Is Organized

The chapters in this book are organized based on a normal JavaScript development life

cycle. This begins, in Chapter 1, with the most optimal ways to load JavaScript onto

the page. Chapter 2 through Chapter 8 focus on specific programming techniques to

help your JavaScript code run as quickly as possible. Chapter 9 discusses the best ways

to build and deploy your JavaScript files to a production environment, and Chap-

ter 10 covers performance tools that can help you identify further issues once the code

is deployed. Five of the chapters were written by contributing authors:

• Chapter 3, DOM Scripting, by Stoyan Stefanov

• Chapter 5, Strings and Regular Expressions, by Steven Levithan

• Chapter 7, Ajax, by Ross Harmes

• Chapter 9, Building and Deploying High-Performance JavaScript Applications, by

Julien Lecomte

• Chapter 10, Tools, by Matt Sweeney

Each of these authors is an accomplished web developer who has made important

contributions to the web development community as a whole. Their names appear on

the opening page of their respective chapters to more easily identify their work.

JavaScript Loading

Chapter 1, Loading and Execution, starts with the basics of JavaScript: getting code

onto the page. JavaScript performance really begins with getting the code onto a page

in the most efficient way possible. This chapter focuses on the performance problems

associated with loading JavaScript code and presents several ways to mitigate the

effects.

Coding Technique

A large source of performance problems in JavaScript is poorly written code that uses

inefficient algorithms or utilities. The following seven chapters focus on identifying

problem code and presenting faster alternatives that accomplish the same task.

Chapter 2, Data Access, focuses on how JavaScript stores and accesses data within a

script. Where you store data is just as important as what you store, and this chapter

explains how concepts such as the scope chain and prototype chain can affect your

overall script performance.

Stoyan Stefanov, who is well versed in the internal workings of a web browser, wrote

Chapter 3, DOM Scripting. Stoyan explains that DOM interaction is slower than other

parts of JavaScript because of the way it is implemented. He covers all aspects of the

DOM, including a description of how repaint and reflow can slow down your code.

xiv | Preface

Chapter 4, Algorithms and Flow Control, explains how common programming para-

digms such as loops and recursion can work against you when it comes to runtime

performance. Optimization techniques such as memoization are discussed, as are

browser JavaScript runtime limitations.

Many web applications perform complex string operations in JavaScript, which is why

string expert Steven Levithan covers the topic in Chapter 5, Strings and Regular Ex-

pressions. Web developers have been fighting poor string-handling performance in

browsers for years, and Steven explains why some operations are slow and how to work

around them.

Chapter 6, Responsive Interfaces, puts the spotlight firmly on the user experience. Java-

Script can cause the browser to freeze as it executes, leaving users extremely frustrated.

This chapter discusses several techniques to ensure that the user interface remains re-

sponsive at all times.

In Chapter 7, Ajax, Ross Harmes discusses the best ways to achieve fast client-server

communication in JavaScript. Ross covers how different data formats can affect Ajax

performance and why XMLHttpRequest isn’t always the best choice.

Chapter 8, Programming Practices, is a collection of best practices that are unique to

JavaScript programming.

Deployment

Once JavaScript code is written and tested, it’s time to make the changes available to

everyone. However, you shouldn’t just push out your raw source files for use in pro-

duction. Julien Lecomte shows how to improve the performance of your JavaScript

during deployment in Chapter 9, Building and Deploying High-Performance JavaScript

Applications. Julien discusses using a build system to automatically minify files and

using HTTP compression to deliver them to the browser.

Testing

When all of your JavaScript code is deployed, the next step is to begin performance

testing. Matt Sweeney covers testing methodology and tools in Chapter 10, Tools. He

discusses how to use JavaScript to measure performance and also describes common

tools both for evaluating JavaScript runtime performance and for uncovering perform-

ance problems through HTTP sniffing.

Who This Book Is For

This book is aimed at web developers with an intermediate-to-advanced understanding

of JavaScript who are looking to improve the performance of web application interfaces.

Preface | xv

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精通高性能JavaScript编程

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