精通JavaScript性能优化

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"High Performance JavaScript，这是一本由 Nicholas C. Zakas 撰写的书籍，主要探讨了如何在JavaScript环境中实现高性能的应用。本书是国外知名的开发参考文档，适合那些希望优化JavaScript性能的开发者阅读。作者 Nicholas C. Zakas 是 Yahoo! 公司的资深工程师，对JavaScript有深入理解和丰富的实践经验。" 在《High Performance JavaScript》一书中，Zakas 提供了一系列实用技巧和最佳实践，帮助开发者提高JavaScript代码的执行效率，减少页面加载时间，提升用户体验。这本书涵盖以下几个核心知识点： 1. **DOM操作优化**：Zakas 强调了高效处理DOM节点的重要性，介绍了批量操作DOM、延迟操作直到DOM加载完成以及使用文档片段等策略来减少DOM操作的开销。 2. **JavaScript性能分析**：他教导读者如何使用浏览器的开发者工具进行性能分析，识别性能瓶颈，并提供了解决这些问题的具体方法。 3. **代码组织与维护**：书中讨论了良好的代码结构和模块化的重要性，如何避免全局变量污染，以及如何使用闭包和立即执行函数表达式（IIFE）来保护作用域。 4. **事件处理**：讲解了如何有效地使用事件处理器，避免内存泄漏，以及使用事件委托来提高性能。 5. **JavaScript对象和数据结构**：深入解析了JavaScript中的对象、数组和哈希表等数据结构，以及如何高效地创建和操作它们。 6. **JavaScript内存管理**：探讨了JavaScript的垃圾回收机制，以及如何避免内存泄漏，确保程序的可持续运行。 7. **函数与作用域**：阐述了函数的内部工作原理，包括作用域链、闭包，以及如何优化函数调用。 8. **异步编程**：讲解了回调函数、Promise和async/await等异步编程技术，以及如何处理异步操作以提高性能。 9. **JavaScript性能最佳实践**：总结了一套适用于各种场景的JavaScript性能优化策略，包括代码压缩、合并和缓存策略。 10. **移动设备上的JavaScript**：针对移动设备的特性，提供了优化JavaScript在移动浏览器上运行的建议。通过学习《High Performance JavaScript》，开发者可以掌握一系列实用的技巧，从而编写出更高效、更健壮的JavaScript代码，提高网页应用的性能，提升用户满意度。这本书不仅是初级开发者提升技能的宝贵资源，也是资深开发者保持与时俱进的必备参考。

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.

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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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