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1．UnderstandingAjaxPerformance1

Trade-offs1

Principles of Optimization1

Ajax4

Browser4

Wow!5

JavaScript6

Summary6

2．CreatingResponsiveWebApplications7

What Is Fast Enough?9

Measuring Latency10

When Latency Goes Bad12

Threading12

Ensuring Responsiveness13

Web Workers14

Gears14

Timers16

Effects of Memory Use on Response Time17

Virtual Memory18

Troubleshooting Memory Issues18

Summary19

3．SplittingtheInitial Payload21

Kitchen Sink21

Savings from Splitting22

Finding the Split23

Undefined Symbols and Race Conditions24

Case Study:Google Calendar25

4．Loading Scripts Without Blocking27

Scripts Block27

Making Scripts Play Nice29

XHR Eval29

XHR Injection31

Script in Iframe31

Script DOM Element32

Script Defer32

document.write Script Tag33

Browser Busy Indicators33

Ensuring(or Avoiding)Ordered Execution35

Summarizing the Results36

And the Winner Is38

5．Coupling Asynchronous Scripts41

Code Example:menu.js42

Race Conditions44

Preserving Order Asynchronously45

Technique 1:Hardcoded Callback46

Technique 2:Window Onload47

Technique 3:Timer48

Technique 4:Script Onload49

Technique 5:Degrading Script Tags50

Multiple External Scripts52

Managed XHR52

DOM Element and Doc Write56

General Solution59

Single Script59

Multiple Scripts60

Asynchronicity in the Real World63

Google Analytics and Dojo63

YUI Loader Utility65

6．Positioning Inline Scripts69

Inline Scripts Block69

Move Inline Scripts to the Bottom70

Initiate Execution Asynchronously71

Use Script Defer73

Preserving CSS and JavaScript Order73

Danger:Stylesheet Followed by Inline Script74

Inline Scripts Aren't Blocked by Most Downloads74

Inline Scripts Are Blocked by Stylesheets75

This Does Happen77

7．Writing Efficient JavaScript79

Managing Scope79

Use Local Variables81

Scope Chain Augmentation83

Efficient Data Access85

Flow Control88

Fast Conditionals89

Fast Loops93

String Optimization99

String Concatenation99

Trimming Strings100

Avoid Long-Running Scripts102

Yielding Using Timers103

Timer Patterns for Yielding105

Summary107

8．Scaling with Comet109

How Comet Works109

Transport Techniques111

Polling111

Long Polling112

Forever Frame113

XHR Streaming115

Future Transports116

Cross-Domain116

Effects of Implementation on Applications118

Managing Connections118

Measuring Performance119

Protocols119

Summary120

9．Going Beyond Gzipping121

Why Does This Matter?121

What Causes This?123

Quick Review123

The Culprit123

Examples of Popular Turtle Tappers124

How to Help These Users?124

Design to Minimize Uncompressed Size125

Educate Users129

Direct Detection of Gzip Support130

10．Optimizing Images133

Two Steps to Simplify Image Optimization134

Image Formats135

Background135

Characteristics of the Different Formats137

More About PNG139

Automated Lossless Image Optimization141

Crushing PNGs142

Stripping JPEG Metadata143

Converting GIF to PNG144

Optimizing GIF Animations144

Smush.it145

Progressive JPEGs for Large Images145

Alpha Transparency:Avoid AlphaImageLoader146

Effects of Alpha Transparency147

AlphaImageLoader149

Problems with AlphaImageLoader150

Progressively Enhanced PNG8 Alpha Transparency151

Optimizing Sprites153

？ber-Sprite Versus Modular Sprite154

Highly Optimized CSS Sprites155

Other Image Optimizations155

Avoid Scaling Images155

Crush Generated Images156

Favicons157

Apple Touch Icon158

Summary159

11．Sharding Dominant Domains161

Critical Path161

Who's Sharding?163

Downgrading to HTTP/1.0165

Rolling Out Sharding168

IP Address or Hostname168

How Many Domains168

How to Split Resources168

Newer Browsers169

12．Flushing the Document Early171

Flush the Head171

Output Buffering173

Chunked Encoding175

Flushing and Gzip176

Other Intermediaries177

Domain Blocking During Flushing178

Browsers:The Last Hurdle178

Flushing Beyond PHP179

The Flush Checklist180

13．Using Iframes Sparingly181

The Most Expensive DOM Element181

Iframes Block Onload182

Parallel Downloads with Iframes184

Script Before Iframe184

Stylesheet Before Iframe185

Stylesheet After Iframe186

Connections per Hostname187

Connection Sharing in Iframes187

Connection Sharing Across Tabs and Windows188

Summarizing the Cost of Iframes190

14．Simplifying CSS Selectors191

Types of Selectors191

ID Selectors192

Class Selectors193

Type Selectors193

Adjacent Sibling Selectors193

Child Selectors193

Descendant Selectors193

Universal Selectors194

Attribute Selectors194

Pseudo-Classes and Pseudo-Elements194

The Key to Efficient CSS Selectors194

Rightmost First195

Writing Efficient CSS Selectors195

CSS Selector Performance197

Complex Selectors Impact Performance(Sometimes)197

CSS Selectors to Avoid200

Reflow Time201

Measuring CSS Selectors in the Real World202

Appendix:Performance Tools205

Index221