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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">3366</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/15530" title="Magento布局layout.xml文件详解" target="_blank" onclick="return recordId('',)">Magento布局layout.xml文件详解 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/15530" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/6.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/15530';}else{window.open('/article/15530');}" style="cursor: pointer;">解析顺序布局xml文件一般位于app/design/{area}/{package}/{theme}/layout/目录下。Layout文件一般包含block、reference、action三种标签。对于Magento系统，首先会将系统中相关相关的layout合并，合并一般是包括app\design\frontend\base\default\layout目录下的xml文件，以及指定的模板下面的对应的layout文件。最终普通网页合并之后的从defaul</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 22:29:49</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3366</span></span>  </p> </article><article class="excerpt"> <header> <a title="Python" class="label label-important zj-del-target" href="/category/44">Python<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/30065" title="python高斯分布概率密度函数的使用详解" target="_blank" onclick="return recordId('',)">python高斯分布概率密度函数的使用详解 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/30065" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/10.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/30065';}else{window.open('/article/30065');}" style="cursor: pointer;">如下所示：importmatplotlib.pyplotaspltimportnumpyasnpfromscipyimportstatsfrommatplotlibimportstylestyle.use('fivethirtyeight')mu_params=[-1,0,1]sd_params=[0.5,1,1.5]x=np.linspace(-7,7,100)f,ax=plt.subplots(len(mu_params),len(sd_params)</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">2019-09-27 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pointer;">出处:http://msdn2.microsoft.com/zh-cn/library/w290k23d(VS.80).aspx全部折叠<styletype="text/css">.vb,.cs,.cpp,.nu{display:none;}</style><styleid="LanguageSpecificTextStyle"type="text/css">.nu{display:inline;}</style>ThispageisspecifictoM</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 23:02:08</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3365</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/10610" title="hadoop namenode多次格式化后，导致datanode启" target="_blank" onclick="return recordId('',)">hadoop namenode多次格式化后，导致datanode启 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/10610" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/14.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/10610';}else{window.open('/article/10610');}" style="cursor: pointer;">jpshadoopnamenode-formatdfsdirectory:/home/hadoop/dfs--data--current/VERSION#WedJul3020:41:03CST2014storageID=DS-ab96ad90-7352-4cd5-a0de-7308c8a358ffclusterID=CID-aa2d4761-974b-4451-8858-bbbcf82e1fd4cTime=0datanodeUuid=a3356a09-78</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 09:27:32</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3365</span></span>  </p> </article><article class="excerpt"> <header> <a title="C#" class="label label-important zj-del-target" 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