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JavaScript 的性能优化：加载和执行

概览无论当前JavaScript代码是内嵌还是在外链文件中，页面的下载和渲染都必须停下来等待脚本执行完成。JavaScript执行过程耗时越久，浏览器等待响应用户输入的时间就越长。浏览器在下载和执行脚本时出现阻塞的原因在于，脚本可能会改变页面或JavaScript的命名空间，它们对后面页面内容造成影响。一个典型的例子就是在页面中使用document.write()。例如清单1清单1JavaScript代码内嵌示例Sou</span> <p class="auth-span"> <span class="muted"><i class="fa fa-user"></i><span class="zj-icon-text">系统</span></span> <span class="muted"><i class="fa fa-clock-o"></i><span class="zj-icon-text">2019-08-29 22:50:45</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3291</span></span>  </p> </article><article class="excerpt"> <header> <a title="IOS" class="label label-important zj-del-target" href="/category/58">IOS<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/17165" title="iOS中编码转化" target="_blank" onclick="return recordId('',)">iOS中编码转化 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/17165" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/8.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/17165';}else{window.open('/article/17165');}" style="cursor: pointer;">iOS中编码转化1.UTF-8转化NSString*data=@"你好，北京！";//转换成UTF-8NSString*dataUTF8=[datastringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];NSLog(@"%@",dataUTF8);//UTF-8转GBK,将UTF8代码替换，官方解释如下。//Replacesallpercentescapeswiththematchin</span> <p class="auth-span"> <span class="muted"><i class="fa fa-user"></i><span class="zj-icon-text">系统</span></span> <span class="muted"><i class="fa fa-clock-o"></i><span class="zj-icon-text">2019-08-29 22:50:23</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3291</span></span>  </p> </article><article class="excerpt"> <header> <a title="Hadoop" class="label label-important zj-del-target" href="/category/60">Hadoop<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/10721" title="《openstack 和hadoop的区别是什么？》" target="_blank" onclick="return recordId('',)">《openstack 和hadoop的区别是什么？》 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/10721" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/18.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/10721';}else{window.open('/article/10721');}" style="cursor: pointer;">openstack和hadoop的区别是什么？（一）openstack仿照的Amazon的云，hadoop仿照的是Google的云openstack注重的是虚拟化/虚拟机及其配套的服务，hadoop注重的是海量的数据分析和处理。（二）2OpenStack主要目的是做一整套的云计算基础构架。包括云计算(Compute),网络(Network)，对象存贮(ObjectStore)，镜像文件存储(Image)，身份认证(Authentication)，Block</span> <p class="auth-span"> <span class="muted"><i class="fa fa-user"></i><span class="zj-icon-text">系统</span></span> <span class="muted"><i class="fa fa-clock-o"></i><span class="zj-icon-text">2019-08-12 09:27:35</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3291</span></span>  </p> </article><article class="excerpt"> <header> <a title="编程技术" class="label label-important zj-del-target" href="/category/30">编程技术<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/22124" title="NPOI根据Excel模板生成原生的Excel文件实例" target="_blank" onclick="return recordId('',)">NPOI根据Excel模板生成原生的Excel文件实例 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/22124" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/1.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/22124';}else{window.open('/article/22124');}" style="cursor: pointer;">上周完成了一个报表小项目，使用开源组件NPOI作为主要组件。之所以采用第三方的开源组件而不使用COM或微软提供的API，原因就不多说了，大家懂的。在此分享NPOI的一个应用，利用Excel模板生成excel文件。这正是NPOI强于Myxls之处。具体步骤如下：一、准备数据USE[MonthReportDemo]GO/******Object:Table[dbo].[TradeReport]ScriptDate:04/15/201119:10:37*****</span> <p class="auth-span"> <span class="muted"><i class="fa fa-user"></i><span class="zj-icon-text">系统</span></span> <span class="muted"><i class="fa fa-clock-o"></i><span class="zj-icon-text">2019-08-29 23:53:33</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3289</span></span>  </p> </article><article class="excerpt"> <header> <a title="C++" class="label label-important zj-del-target" href="/category/42">C++<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/19735" title="C++学习笔记(五)--虚函数表解析" target="_blank" onclick="return recordId('',)">C++学习笔记(五)--虚函数表解析 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/19735" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/2.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/19735';}else{window.open('/article/19735');}" style="cursor: pointer;">前言C++中的虚函数的作用主要是实现了多态的机制。关于多态，简而言之就是用父类型别的指针指向其子类的实例，然后通过父类的指针调用实际子类的成员函数。这种技术可以让父类的指针有“多种形态”，这是一种泛型技术。所谓泛型技术，说白了就是试图使用不变的代码来实现可变的算法。比如：模板技术，RTTI技术，虚函数技术，要么是试图做到在编译时决议，要么试图做到运行时决议。关于虚函数的使用方法，我在这里不做过多的阐述。大家可以看看相关的C++的书籍。在这篇文章中，我只想从</span> <p class="auth-span"> <span class="muted"><i class="fa fa-user"></i><span class="zj-icon-text">系统</span></span> <span class="muted"><i class="fa fa-clock-o"></i><span class="zj-icon-text">2019-08-29 23:23:28</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3289</span></span>  </p> </article><div class="pagination" style="display:;"> <ul><li><a href="/search/oom/1/p/1">首页</a></li> <li class="prev-page"><a 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