[翻译]High Performance JavaScript(030)
第十章 Tools 工具
Having the right software is essential for identifying bottlenecks in both the loading and running of scripts. A number of browser vendors and large-scale websites have shared techniques and tools to help make the Web faster and more efficient. This chapter focuses on some of the free tools available for:
当确定脚本加载和运行时的瓶颈所在时，合手的工具是必不可少的。许多浏览器厂商和大型网站分享了一些技术和工具，帮助开发者使网页更快，效率更高。本章关注于这些免费工具：
Profiling 性能分析
Timing various functions and operations during script execution to identify areas for optimization
在脚本运行期定时执行不同函数和操作，找出需要优化的部分
Network analysis 网络分析
Examining the loading of images, stylesheets, and scripts and their effect on overall page load and rendering
检查图片，样式表，和脚本的加载过程，汇报它们对整个页面加载和渲染的影响
When a particular script or application is performing less than optimally, a profiler can help prioritize areas for optimization. This can get tricky because of the range of supported browsers, but many vendors now provide a profiler along with their debugging tools. In some cases, performance issues may be specific to a particular browser; other times, the symptoms may occur across multiple browsers. Keep in mind that the optimizations applied to one browser might benefit other browsers, but they might have the opposite effect as well. Rather than assuming which functions or operations are slow, profilers ensure that optimization time is spent on the slowest areas of the system that affect the most browsers.
当一个特定的脚本或应用程序没有达到最优状态时，一个性能分析器有助于安排优化工作的先后次序。不过，因为浏览器支持的范围不同，这可能变得很麻烦，但许多厂商在他们的调试工具中提供了性能分析器。有些情况下，性能问题可能与特定浏览器
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使用javascript创建Microsoft XML DOM,就可以完成这一工作.
// 装入数据.
var source = new ActiveXObject("Microsoft.XMLDOM");
source.async = false
source.load("history.xml");
// 装入样式表.
var stylesheet = new ActiveXObject("Microsoft.XMLDOM");
stylesheet.async = false
stylesheet.load( ......
function total(){
var i=0;
for(j=1;j<=20;j++)
{
var step="step"+j;
if(document.getElementById(step)){
if(document.getElementById(step).checked==true)
{
i=i+parseInt(document.getElementById(step).value);
}
}
}
document.getElementById("total").innerHTML = i;
}
function Resetvalue(){
......
第四章 Algorithms and Flow Control 算法和流程控制
The overall structure of your code is one of the main determinants as to how fast it will execute. Having a very small amount of code doesn't necessarily mean that it will run quickly, and having a large amount of code ......
A Note on Benchmarking 测试基准说明
Because a regex's performance can be wildly different depending on the text it's applied to, there's no straightforward way to benchmark regexes against each other. For the best result, you need to benchmark your regexes on test strings o ......
第九章
Building and Deploying High-Performance JavaScript Applications
创建并部署高性能JavaScript应用程序
According to a 2007 study by Yahoo!'s Exceptional Performance team, 40%–60% of Yahoo!'s users have an empty cache experience, and about 20% of all page views are done ......
