对于任何成功的网站来说，性能是至关重要的。但伴随着不断增长的丰富内容和Ajax的过度使用，如今的Web应用已经将浏览器推至性能极限。在本书中，Google的Web性能专家和前任雅虎首席网站性能官Steve Souders提供了宝贵的技术，来帮助你优化网站性能。

作者的上一本书是非常畅销的《High Performance Web Sites》，它透露了80%的网页加载时间是花在客户端，使网络开发世界为之震惊。在本书中，Souders和8位专家撰稿人提供了最佳实践和实用建议，用于在三个范畴提高网站的性能：

JavaScript——获取用于了解Ajax性能的建议，编写有效的JavaScript，创建响应程序，加载脚本时不阻止其他组件等等。

Network——学习穿过多个域共享资源，减小图片尺寸而不损失质量，以及使用分块编码(chunked encoding)来更快呈现页面。

Browser——探索内嵌框架(iframe)的替代方案、如何简化CSS选择器和其他技术。

对于当今的富媒体网站和Web 2.0应用来说，速度是至关重要的。有了这本书，你将学习到如何减少你的网站的加载时间，让它们响应得更快。

Credits

Preface

1. Understanding Ajax Performance

 Trade-offs

 Principles of Optimization

 Ajax

 Browser

 Wow!

 JavaScript

 Summary

2. Creating Responsive Web Applications

 What Is Fast Enough?

 Measuring Latency

When Latency Goes Bad

 Threading

 Ensuring Responsiveness

Web Workers

Gears

Timers

Effects of Memory Use on Response Time

Virtual Memory

Troubleshooting Memory Issues

 Summary

3. Splitting the Initial Payload

 Kitchen Sink

 Savings from Splitting

 Finding the Split

 Undefined Symbols and Race Conditions

 Case Study: Google Calendar

4. Loading Scripts Without Blocking

 Scripts Block

 Making Scripts Play Nice

 XHR Eval

XHR Injection

Script in Iframe

Script DOM Element

Script Defer

document.write Script Tag

 Browser Busy Indicators

 Ensuring (or Avoiding) Ordered Execution

 Summarizing the Results

 And the Winner Is

5. Coupling Asynchronous Scripts

 Code Example: menu.js

 Race Conditions

 Preserving Order Asynchronously

Technique 1: Hardcoded Callback

Technique 2: Window Onload

Technique 3: Timer

Technique 4: Script Onload

Technique 5: Degrading Script Tags

 Multiple External Scripts

Managed XHR

DOM Element and Doc Write

 General Solution

Single Script

Multiple Scripts

 Asynchronicity in the Real World

Google Analytics and Dojo

YUI Loader Utility

6. Positioning Inline Scripts

 Inline Scripts Block

Move Inline Scripts to the Bottom

Initiate Execution Asynchronously

Use Script Defer

 Preserving CSS and JavaScript Order

 Danger: Stylesheet Followed by Inline Script

Inline Scripts Aren’t Blocked by Most Downloads

Inline Scripts Are Blocked by Stylesheets

This Does Happen

7. Writing Efficient JavaScript

 Managing Scope

Use Local Variables

Scope Chain Augmentation

 Efficient Data Access

 Flow Control

Fast Conditionals

Fast Loops

 String Optimization

String Concatenation

Trimming Strings

 Avoid Long-Running Scripts

Yielding Using Timers

Timer Patterns for Yielding

 Summary

8. Scaling with Comet

 How Comet Works

 Transport Techniques

Polling

Long Polling

Forever Frame

XHR Streaming

Future Transports

 Cross-Domain

 Effects of Implementation on Applications

Managing Connections

Measuring Performance

Protocols

 Summary

9. Going Beyond Gzipping

 Why Does This Matter?

 What Causes This?

Quick Review

The Culprit

Examples of Popular Turtle Tappers

 How to Help These Users?

Design to Minimize Uncompressed Size

Educate Users

Direct Detection of Gzip Support

10. Optimizing Images

 Two Steps to Simplify Image Optimization

 Image Formats

Background

Characteristics of the Different Formats

More About PNG

 Automated Lossless Image Optimization

Crushing PNGs

Stripping JPEG Metadata

Converting GIF to PNG

Optimizing GIF Animations

Smush.it

Progressive JPEGs for Large Images

 Alpha Transparency: Avoid AlphaImageLoader

Effects of Alpha Transparency

AlphaImageLoader

Problems with AlphaImageLoader

Progressively Enhanced PNG8 Alpha Transparency

 Optimizing Sprites

ǖber-Sprite Versus Modular Sprite

Highly Optimized CSS Sprites

 Other Image Optimizations

Avoid Scaling Images

Crush Generated Images

Favicons

Apple Touch Icon

 Summary

11. Sharding Dominant Domains

 Critical Path

 Who’s Sharding?

 Downgrading to HTTP/1.0

 Rolling Out Sharding

IP Address or Hostname

How Many Domains

How to Split Resources

Newer Browsers

12. Flushing the Document Early

 Flush the Head

 Output Buffering

 Chunked Encoding

 Flushing and Gzip

 Other Intermediaries

 Domain Blocking During Flushing

 Browsers: The Last Hurdle

 Flushing Beyond PHP

 The Flush Checklist

13. Using Iframes Sparingly

 The Most Expensive DOM Element

 Iframes Block Onload

 Parallel Downloads with Iframes

Script Before Iframe

Stylesheet Before Iframe

Stylesheet After Iframe

 Connections per Hostname

Connection Sharing in Iframes

Connection Sharing Across Tabs and Windows

 Summarizing the Cost of Iframes

14. Simplifying CSS Selectors

 Types of Selectors

ID Selectors

Class Selectors

Type Selectors

Adjacent Sibling Selectors

Child Selectors

Descendant Selectors

Universal Selectors

Attribute Selectors

Pseudo-Classes and Pseudo-Elements

 The Key to Efficient CSS Selectors

Rightmost First

Writing Efficient CSS Selectors

 CSS Selector Performance

Complex Selectors Impact Performance (Sometimes)

CSS Selectors to Avoid

Reflow Time

 Measuring CSS Selectors in the Real World

Appendix: Performance Tools

Index