[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
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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(){
......
Conditionals 条件表达式
Similar in nature to loops, conditionals determine how execution flows through JavaScript. The traditional argument of whether to use if-else statements or a switch statement applies to JavaScript just as it does to other languages. Since different b ......
Splitting Up Tasks 分解任务
What we typically think of as one task can often be broken down into a series of subtasks. If a single function is taking too long to execute, check to see whether it can be broken down into a series of smaller functions that complete in smaller ......
Data Format Conclusions 数据格式总结
Favor lightweight formats in general; the best are JSON and a character-delimited custom format. If the data set is large and parse time becomes an issue, use one of these two techniques:
总的来说越轻量级的格式越好，� ......
