[翻译]High Performance JavaScript(029)
Working Around Caching Issues 关于缓存问题
Adequate cache control can really enhance the user experience, but it has a downside: when revving up your application, you want to make sure your users get the latest version of the static content. This is accomplished by renaming static resources whenever they change.
充分利用缓存控制可真正提高用户体验，但它有一个缺点：当应用程序更新之后，你希望确保用户得到静态内容的最新版本。这通过对改动的静态资源进行重命名实现。
Most often, developers add a version or a build number to filenames. Others like to append a checksum. Personally, I like to use a timestamp. This task can be automated using Ant. The following target takes care of renaming JavaScript files by appending a timestamp in the form of yyyyMMddhhmm:
大多情况下，开发者向文件名中添加一个版本号或开发编号。有人喜欢追加一个校验和。个人而言，我更喜欢时间戳。此任务可用Ant自动完成。下面的目标体通过附加一个yyyyMMddhhmm格式的时间戳重名名JavaScript文件：
<target name="js.copy">
<!-- Create the time stamp -->
<tstamp/>
<!-- Rename JavaScript files by appending a time stamp -->
<copy todir="${build.dir}">
<fileset dir="${src.dir}" includes="*.js"/>
<globmapper from="*.js" to="*-${DSTAMP}${TSTAMP}.js"/>
</copy>
</target>
Using a Content Delivery Network 使用内容传递网
A content delivery network (CDN) is a network of computers distributed geographically across the Internet that is responsible for delivering content to end users. The primary reasons for using a CDN are reliability, scalability, and above all, performance. In fact, by serving content from the location closest to the user, CDNs are able to dramatically decrease network latency.
内容传递网络（CDN）是按照地理分布的计算机网络，通过以太网负责向最终用户分
相关文档：
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( ......
AJAX (异步 JavaScript 和 XML) 是个新产生的术语,专为描述JavaScript的两项强大性能.这两项性
能在多年来一直被网络开发者所忽略,直到最近Gmail, Google suggest和google Maps的横空出世才使人
们开始意识到其重要性.
这两项被忽视的性能是:
* 无需重新装载整个页面便能向服务器发送请求.
* 对XML文档的解析和处理．
......
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(){
......
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 ......
Yielding with Timers 用定时器让出时间片
Despite your best efforts, there will be times when a JavaScript task cannot be completed in 100 milliseconds or less because of its complexity. In these cases, it's ideal to yield control of the UI thread so that UI updates may occur ......
