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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">3201</span></span>  </p> </article><article class="excerpt"> <header> <a title="Android" class="label label-important zj-del-target" href="/category/57">Android<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/14933" title="【Android 开发教程】保存到外部存储设备（SD卡" target="_blank" onclick="return recordId('',)">【Android 开发教程】保存到外部存储设备（SD卡 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/14933" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/15.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/14933';}else{window.open('/article/14933');}" style="cursor: pointer;">本章节翻译自《Beginning-Android-4-Application-Development》，如有翻译不当的地方，敬请指出。原书购买地址http://www.amazon.com/Beginning-Android-4-Application-Development/dp/1118199545/上一节介绍了如何把文件存储到内部设备。有的时候，需要把文件存储到外部存储设备，比如SD卡。因为SD卡具有更大的存储空间，同时也可以很容易的和其他用户分享这</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 22:22:02</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3201</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/12199" title="微软新推TypeScript取代JavaScript" target="_blank" onclick="return recordId('',)">微软新推TypeScript取代JavaScript </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/12199" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/12.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/12199';}else{window.open('/article/12199');}" style="cursor: pointer;">微软新推TypeScript取代JavaScriptTypeScript是一个应用程序级的JavaScript开发语言。TypeScript是JavaScript的超集，可以编译成纯JavaScript。TypeScript跨浏览器、跨操作系统、跨主机，开源。主页：http://www.typescriptlang.org/StartsfromJavaScript,EndswithJavaScriptTypeScript遵循JavaScript的语法和语义</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 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pointer;">VisualLeakDetectorforVisualC++2008/2010/2012VisualLeakDetectorforVisualC++2008/2010/2012ProjectDescriptionVisualLeakDetectorisafree,robust,open-sourcememoryleakdetectionsystemforVisualC++.It'sprettyeasytouse.Afterinstallingit,youj</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 01:32:41</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3201</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/21061" title="Registering JavaScript object methods as cal" target="_blank" onclick="return recordId('',)">Registering JavaScript object methods as cal </a> </h2> </header> <div class="focus"> <a 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