高性能网站(英文影印版)

　　
　　《高性能网站》中的规則向你解释了可以怎样优化网站中包含的ajax、css、javascript、flash和图片。每个规则都可以在本书的网站上找到对应的特别例子和代码片段。这些规則包括以下内容：减少http连接请求、使用内容分发网络(contentdeliverynetwork)、在http协议头添加过期时间、把部分内容变成gzip格式、把样式表(stylesheets)放在顶部、将脚本放在底部、避免css表达式、外置javascript和css、减少dns查找、将javascript最小化、避免重定向连接、删除重复脚本、配置etags、生成可缓冲ajax、
　　 如果你在为大流量的站点编写网页并且想要优化站点访问的用户体验，这本书不可或缺。
　　

foreword
preface
a. the importance of frontend performance
tracking web page performance
where does the time go?
the performance golden rule
b. http overview
compression
conditional get requests
expires
keep-alive
there's more
1. rule 1: make fewer http requests
image maps
css sprites
inline images
combined scripts and stylesheets
conclusion
2. rule 2: use a content delivery network

　　In eighth grade, my history class studied the efficiency experts of the Industrial Revolution. I was enthralled by the techniques they used to identify and overcome bottle-necks in manufacturing. The most elegant improvement, in my mind, was the adjustable stepstool that afforded workers of different heights the ability to more easily reach the conveyor belt--a simple investment that resulted in improved performance for the life of the process. .
　　Three decades later, I enjoy comparing the best practices in this book to that 19th-century stepstool. These best practices enhance an existing process. They require some upfront investment, but the cost is small--especially in comparison to the gains. And once these improvements are put in place, they continue to boost performance over the life of the development process. I hope you'll find these rules for building high performance web sites to be elegant improvements that benefit you and your users.
　　How This Book Is Organized
　　After two quick introductory chapters, I jump into the main part of this book: the 14 performance rules. Each rule is described, one per chapter, in priority order. Not every rule applies to every site, and not every site should apply a rule the same way, but each is worth considering. The final chapter of this book shows how to analyze web pages from a performance perspective, including some case studies.
　　Chapter A, The Importance of Frontend Performance explains that at least 80 percent of the time it takes to display a web page happens after the HTML document has been downloaded, and describes the importance of the techniques in this book.
　　Chapter B, HTTP Overview provides a short description of HTTP, highlighting the parts that are relevant to performance.
　　Chapter 1, Rule 1: Make Fewer HTTP Requests describes why extra HTTP requests have the biggest impact on performance, and discusses ways to reduce these HTTP requests including image maps, CSS sprites, inline images using data: URLs, and combining scripts and stylesheets.
　　Chapter 2, Rule 2: Use a Content Delivery Network highlights the advantages of using a content delivery network.
　　Chapter 3, Rule 3: Add an Expires Header digs into how a simple HTTP header dramatically improves your web pages by using the browser's cache.
　　Chapter 4, Rule 4: Gzip Components explains how compression works and how to enable it for your web servers, and discusses some of the compatibility issues that exist today.
　　Chapter 5, Rule 5: Put Stylesheets at the Top reveals how stylesheets affect the rendering of your page.
　　Chapter 6, Rule 6: Put Scripts at the Bottom shows how scripts affect rendering and downloading in the browser.
　　Chapter 7, Rule 7: Avoid CSS Expressions discusses the use of CSS expressions and the importance of quantifying their impact.
　　Chapter 8, Rule 8: Make JavaScript and CSS External talks about the tradeoffs of inlining your JavaScript and CSS versus putting them in external files.
　　Chapter 9, Rule 9: Reduce DNS Lookups highlights the often-overlooked impact of resolving domain names.
　　Chapter 10, Rule 10: Minify JavaScript quantifies the benefits of removing whitespace from your JavaScript.
　　Chapter 11, Rule 11: Avoid Redirects warns against using redirects, and provides alternatives that you can use instead.
　　Chapter 12, Rule 12: Remove Duplicate Scripts reveals what happens if a script is included twice in a page.
　　Chapter 13, Rule 13: Configure ETags describes how ETags work and why the default implementation is bad for anyone with more than one web server.
　　Chapter 14, Rule 14: Make Ajax Cacheable emphasizes the importance of keeping these performance rules in mind when using Ajax. ..

　　You're lucky to be holding this book. More importantly, your web site's users are lucky. Implement even a few of the 14 techniques Steve shares in this groundbreaking book and your site will be faster immediately. Your users will thank you. .
　　Here is why it matters. As a frontend engineer, you hold a tremendous amount of power and responsibility. You're the users' last line of defense. The decisions you make directly shape their experience. I believe our number one job is to take care of them and to give them what they want--quickly. This book is a toolbox to create happy users (and bosses, too). Best of all, once you put these techniques in place--in most cases, a one-time tweak--you'll be reaping the rewards far into the future.
　　This book will change your approach to performance optimization. When Steve began researching performance for our Platform Engineering group at Yahoo!, I believed performance was mainly a backend issue. But he showed that frontend issues account for 80% of total time. I thought frontend performance was about optimizing images and keeping CSS and JavaScript external, but the 176 pages and 14 rules you're holding in your hand right now are proof that it's much more. ..
　　I've applied his findings to several sites. Watching already-fast sites render nearly twice as quickly is tremendous. His methodology is sound, his data valid and extensive, and his findings compelling and impactful.
　　The discipline of frontend engineering is still young, but the book in your hands is an important step in the maturation of our craft. Together we'll raise expectations about the Web by creating better and faster (and therefore more enjoyable) interfaces and experiences.
　　Cheers to faster surfing! ...
　　--Nate Koechtey
　　Senior Frontend Engineer
　　Yahoo! User Interface (YUI) Team, Platform
　　Engineering, Yahoo! Inc.
　　San Francisco, August, 2007
　　

　　“假如每个人都实施Steve书中20％的规则，那么互联网将会是个更好些的地方。有了本书和Steve的YSlow扩展程序，再也没有理由为一个性能低下的网站找借口。”.
　　——Joe Hewitt，Firebug调试器和Mozilla的DOM查看器的开发人员..
　　
　　“Steve Souders完成了令人难以置信的工作，把一门宽泛且半秘密的艺术提炼成一套简明扼要且具有可操作性的实际工程步骤，这些步骤将会改变网络性能的世界。”
　　——Eric Lawrence，Fiddle Web Debugger开发人员，微软...