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High Performance JavaScript
Table of Contents
Preface ..................................................................... xi
1. Loading and Execution ................................................... 1
Script Positioning 2
Grouping Scripts 4
Nonblocking Scripts 5
Deferred Scripts 5
Dynamic Script Elements 6
XMLHttpRequest Script Injection 9
Recommended Nonblocking Pattern 10
Summary 14
2. Data Access ........................................................... 15
Managing Scope 16
Scope Chains and Identifier Resolution 16
Identifier Resolution Performance 19
Scope Chain Augmentation 21
Dynamic Scopes 24
Closures, Scope, and Memory 24
Object Members 27
Prototypes 27
Prototype Chains 29
Nested Members 30
Caching Object Member Values 31
Summary 33
3. DOM Scripting ......................................................... 35
DOM in the Browser World 35
Inherently Slow 36
DOM Access and Modification 36
innerHTML Versus DOM methods 37
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Cloning Nodes 41
HTML Collections 42
Walking the DOM 46
Repaints and Reflows 50
When Does a Reflow Happen? 51
Queuing and Flushing Render Tree Changes 51
Minimizing Repaints and Reflows 52
Caching Layout Information 56
Take Elements Out of the Flow for Animations 56
IE and :hover 57
Event Delegation 57
Summary 59
4. Algorithms and Flow Control ............................................. 61
Loops 61
Types of Loops 61
Loop Performance 63
Function-Based Iteration 67
Conditionals 68
if-else Versus switch 68
Optimizing if-else 70
Lookup Tables 72
Recursion 73
Call Stack Limits 74
Recursion Patterns 75
Iteration 76
Memoization 77
Summary 79
5. Strings and Regular Expressions .......................................... 81
String Concatenation 81
Plus ( ) and Plus-Equals ( =) Operators 82
Array Joining 84
String.prototype.concat 86
Regular Expression Optimization 87
How Regular Expressions Work 88
Understanding Backtracking 89
Runaway Backtracking 91
A Note on Benchmarking 96
More Ways to Improve Regular Expression Efficiency 96
When Not to Use Regular Expressions 99
String Trimming 99
Trimming with Regular Expressions 99
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Trimming Without Regular Expressions 102
A Hybrid Solution 103
Summary 104
6. Responsive Interfaces ................................................. 107
The Browser UI Thread 107
Browser Limits 109
How Long Is Too Long? 110
Yielding with Timers 111
Timer Basics 112
Timer Precision 114
Array Processing with Timers 114
Splitting Up Tasks 116
Timed Code 118
Timers and Performance 119
Web Workers 120
Worker Environment 120
Worker Communication 121
Loading External Files 122
Practical Uses 122
Summary 124
7. Ajax ................................................................ 125
Data Transmission 125
Requesting Data 125
Sending Data 131
Data Formats 134
XML 134
JSON 137
HTML 141
Custom Formatting 142
Data Format Conclusions 144
Ajax Performance Guidelines 145
Cache Data 145
Know the Limitations of Your Ajax Library 148
Summary 149
8. Programming Practices ................................................ 151
Avoid Double Evaluation 151
Use Object/Array Literals 153
Don’t Repeat Work 154
Lazy Loading 154
Conditional Advance Loading 156
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Use the Fast Parts 156
Bitwise Operators 156
Native Methods 159
Summary 161
9. Building and Deploying High-Performance JavaScript Applications ........... 163
Apache Ant 163
Combining JavaScript Files 165
Preprocessing JavaScript Files 166
JavaScript Minification 168
Buildtime Versus Runtime Build Processes 170
JavaScript Compression 170
Caching JavaScript Files 171
Working Around Caching Issues 172
Using a Content Delivery Network 173
Deploying JavaScript Resources 173
Agile JavaScript Build Process 174
Summary 175
10. Tools ................................................................ 177
JavaScript Profiling 178
YUI Profiler 179
Anonymous Functions 182
Firebug 183
Console Panel Profiler 183
Console API 184
Net Panel 185
Internet Explorer Developer Tools 186
Safari Web Inspector 188
Profiles Panel 189
Resources Panel 191
Chrome Developer Tools 192
Script Blocking 193
Page Speed 194
Fiddler 196
YSlow 198
dynaTrace Ajax Edition 199
Summary 202
Index ..................................................................... 203