《Even Faster Web Sites》Steve Souders 高性能网站建设指南

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"高性能网站建设进阶指南 - Steve Souders" 《高性能网站建设进阶指南》是Steve Souders的作品，该书深入探讨了如何优化网站性能，以提供更快、更流畅的用户体验。书中涵盖了一系列关键知识点，旨在帮助开发者构建速度更快、效率更高的网页。 1. **最小化HTTP请求**：一个页面的加载速度往往受限于它需要进行的HTTP请求数量。Steve Souders强调减少HTTP请求可以显著提高页面加载速度。这包括合并CSS和JavaScript文件，以及使用CSS Sprites来减少图像请求。 2. **优化CSS和JavaScript**：压缩代码可以减小文件大小，从而加快下载速度。书中有详细的方法介绍如何去除代码中的空格、换行和注释，以及如何利用Gzip等工具进行压缩。 3. **利用缓存**：通过设置正确的HTTP头信息，可以让浏览器缓存静态资源，减少不必要的网络请求，提升用户体验。 4. **减少DNS查找**：每个域名解析都需要DNS查找时间，所以减少页面中不同域名的数量能减少总查找时间，加快页面加载。 5. **延迟加载非关键内容**：使用异步加载或懒加载技术，只在用户滚动到相关内容时才加载图片或其他非关键元素，可以提高首屏加载速度。 6. **优化图片**：合理使用JPEG、PNG、SVG等格式，根据需要选择压缩级别，并利用CSS Sprites技术，可以有效降低图片加载时间。 7. **减少重定向**：重定向会增加额外的HTTP请求和响应时间，应避免不必要的重定向，尤其是在首页。 8. **预加载和预读取**：通过预加载技术，可以提前加载用户可能需要的资源，预读取则可以提前解析但不下载，以减少延迟。 9. **启用HTTP/2**：相比于HTTP/1.1，HTTP/2支持多路复用，允许同时发送多个请求和响应，显著减少了页面加载时间。 10. **使用CDN（内容分发网络）**：通过将静态资源放在全球各地的服务器上，CDN可以减少网络延迟，加快内容的传输速度。 11. **移动优先**：随着移动设备的普及，设计和优化针对移动用户的网站成为关键，采用移动优先的策略能确保所有用户都能快速访问。 12. **监控和测量性能**：定期使用工具如PageSpeed Insights、WebPageTest等评估和分析网站性能，以便持续优化。 Steve Souders的这本书不仅提供了理论知识，还包含了许多实用技巧和案例研究，对于任何想要提升网站性能的开发者来说，都是一本宝贵的参考书。通过实践这些最佳实践，开发者可以构建出更快、更高效的网站，提供更佳的用户体验。

• Rule 5: Put Stylesheets at the Top

• Rule 6: Put Scripts at the Bottom

• Rule 7: Avoid CSS Expressions

• Rule 8: Make JavaScript and CSS External

• Rule 9: Reduce DNS Lookups

• Rule 10: Minify JavaScript

• Rule 11: Avoid Redirects

• Rule 12: Remove Duplicate Scripts

• Rule 13: Configure ETags

• Rule 14: Make Ajax Cacheable

I call them “rules” because there is little ambiguity about their adoption. Consider these

statistics for the top 10 U.S. web sites

for March 2007:

• Two sites used CSS sprites.

• 26% of resources had a future Expires header.

• Five sites compressed their HTML, JavaScript, and CSS.

• Four sites minified their JavaScript.

The same statistics for April 2009 show that these rules are gaining traction:

• Nine sites use CSS sprites.

• 93% of resources have a future Expires header.

• Ten sites compress their HTML, JavaScript, and CSS.

• Nine sites minify their JavaScript.

The rules from High Performance Web Sites still apply and are where most web com-

panies should start. Progress is being made, but there’s still more work to be done on

this initial set of rules.

But the Web isn’t standing still, waiting for us to catch up. Although the 14 rules from

High Performance Web Sites still apply, the growth in web page content and Web 2.0

applications introduces a new set of performance challenges. Even Faster Web Sites

provides the best practices needed by developers to make these next-generation web

sites faster.

The chapters in this book are organized into three areas: JavaScript performance

(Chapters 1–7), network performance (Chapters 8–12), and browser performance

(Chapters 13 and 14). A roundup of the best tools for analyzing performance comes in

the Appendix.

AOL, eBay, Facebook, Google Search, Live Search, MSN.com, MySpace, Wikipedia, Yahoo!, and YouTube,

according to Alexa.

xiv | Preface

Six of the chapters were written by contributing authors:

• Chapter 1, Understanding Ajax Performance, by Douglas Crockford

• Chapter 2, Creating Responsive Web Applications, by Ben Galbraith and Dion

Almaer

• Chapter 7, Writing Efficient JavaScript, by Nicholas C. Zakas

• Chapter 8, Scaling with Comet, by Dylan Schiemann

• Chapter 9, Going Beyond Gzipping, by Tony Gentilcore

• Chapter 10, Optimizing Images, by Stoyan Stefanov and Nicole Sullivan

These authors are experts in each of these areas. I wanted you to hear from them

directly, in their own voices. To help identify these chapters, the name(s) of the con-

tributing author(s) are on the chapter’s opening page.

JavaScript Performance

In my work analyzing today’s web sites, I consistently see that JavaScript is the key to

better-performing web applications, so I’ve started the book with these chapters.

Douglas Crockford wrote Chapter 1, Understanding Ajax Performance. Doug describes

how Ajax changes the way browsers and servers interact, and how web developers need

to understand this new relationship to properly identify opportunities for improving

performance.

Chapter 2, Creating Responsive Web Applications, by Ben Galbraith and Dion Almaer,

ties JavaScript performance back to what really matters: the user experience. Today’s

web applications invoke complex functions at the click of a button and must be eval-

uated on the basis of what they’re forcing the browser to do. The web applications that

succeed will be written by developers who understand the effects of their code on

response time.

I wrote the next four chapters. They focus on the mechanics of JavaScript—the best

way to package it and load it, and where to insert it in your pages. Chapter 3, Splitting

the Initial Payload, describes the situation facing many web applications today: a huge

JavaScript download at the beginning of the page that blocks rendering as well as further

downloads. The key is to break apart this monolithic JavaScript for more efficient

Chapters 4 and 5 go together. In today’s most popular browsers, external scripts block

everything else in the page. Chapter 4, Loading Scripts Without Blocking, explains how

to avoid these pitfalls when loading external scripts. Loading scripts asynchronously

presents a challenge when inlined code depends on them. Luckily, there are several

techniques for coupling inlined code with the asynchronous scripts on which they de-

pend. These techniques are presented in Chapter 5, Coupling Asynchronous Scripts.

Preface | xv

Chapter 6, Positioning Inline Scripts, presents performance best practices that apply to

inline scripts, especially the impact they have on blocking parallel downloads.

I think of Chapter 7, Writing Efficient JavaScript, written by Nicholas C. Zakas, as the

complement to Doug’s chapter (Chapter 1). Whereas Doug describes the Ajax land-

scape, Nicholas zooms in on several specific techniques for speeding up JavaScript.

Network Performance

Web applications aren’t desktop applications—they have to be downloaded over the

Internet each time they are used. The adoption of Ajax has resulted in a new style of

data communication between servers and clients. Some of the biggest opportunities for

growth in the web industry are in emerging markets where Internet connectivity is a

challenge, to put it mildly. All of these factors highlight the need for improved network

performance.

In Chapter 8, Scaling with Comet, Dylan Schiemann describes an architecture that goes

beyond Ajax to provide high-volume, low-latency communication for real-time appli-

cations such as chat and document collaboration.

Chapter 9, Going Beyond Gzipping, describes how turning on compression isn’t enough

to guarantee optimal delivery of your web site’s content. Tony Gentilcore reveals a

little-known phenomenon that severely hinders the network performance of 15% of

the world’s Internet users.

Stoyan Stefanov and Nicole Sullivan team up to contribute Chapter 10, Optimizing

Images. This is a thorough treatment of the topic. This chapter reviews all popular

image formats, presents numerous image optimization techniques, and describes the

image compression tools of choice.

The remaining chapters were written by me. Chapter 11, Sharding Dominant Do-

mains, reminds us of the connection limits in the popular browsers of today, as well as

the next generation of browsers. It includes techniques for successfully splitting

resources across multiple domains.

Chapter 12, Flushing the Document Early, walks through the benefits and many gotchas

of using chunked encoding to start rendering the page even before the full HTML

document has arrived.

Browser Performance

Iframes are an easy and frequently used technique for embedding third-party content

in a web page. But they come with a cost. Chapter 13, Using Iframes Sparingly, explains

the downsides of iframes and offers a few alternatives.

Chapter 14, Simplifying CSS Selectors, presents the theories about how complex selec-

tors can impact performance, and then does an objective analysis to pinpoint the

situations that are of most concern.

xvi | Preface

To comment or ask technical questions about this book, send email to:

bookquestions@oreilly.com

For more information about our books, conferences, Resource Centers, and the

O’Reilly Network, see our web site at:

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Using Code Examples

You may use the code in this book in your programs and documentation. You do not

need to contact us for permission unless you’re reproducing a significant portion of the

code. For example, writing a program that uses several chunks of code from this book

does not require permission. Selling or distributing a CD-ROM of examples from this

book does require permission. Answering a question by citing this book and quoting

example code does not require permission. Incorporating a significant amount of ex-

ample code from this book into your product’s documentation does require permission.

We appreciate, but do not require, attribution. An attribution usually includes the title,

author, publisher, and ISBN. For example: “Even Faster Web Sites, by Steve Souders.

If you feel your use of code examples falls outside fair use or the permission given above,

feel free to contact us at permissions@oreilly.com.

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Acknowledgments

I first want to thank the contributing authors: Dion Almaer, Doug Crockford, Ben

Galbraith, Tony Gentilcore, Dylan Schiemann, Stoyan Stefanov, Nicole Sullivan, and

Nicholas Zakas. They’ve made this a special book. Each of them is an expert in his or

her own right. Most of them have written their own books. By sharing their expertise,

they’ve helped create something unique.

xviii | Preface

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《Even Faster Web Sites》Steve Souders 高性能网站建设指南

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