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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">3504</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/15538" title="君正4750开发板使用日记6-uCOS(minios)的开发配" target="_blank" onclick="return recordId('',)">君正4750开发板使用日记6-uCOS(minios)的开发配 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/15538" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/11.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/15538';}else{window.open('/article/15538');}" style="cursor: pointer;">大半年没有搞君正的开发板了，最近总算有机会再试试JZ4750的uc/osII配置。也在此做个记录，供参阅。ucos要在linux环境下编译，我仍是在windows下用VMWareUbuntuServer910虚拟机，用Putty连接登录后执行命令。我一开始并没有拿到了JZ4750的ucos的SDK（随机光盘上只有一个可烧录的DEMO），于是从君正官网的FTP里下载了Jz-uCOS-Development-guide.pdf、mipsel-4.1.2-nop</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 22:29:54</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3504</span></span>  </p> </article><article class="excerpt"> <header> <a title="Hive" class="label label-important zj-del-target" href="/category/59">Hive<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/9395" title="hive中的subkeylist的结构详解。。" target="_blank" onclick="return recordId('',)">hive中的subkeylist的结构详解。。 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/9395" 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/9395';}else{window.open('/article/9395');}" style="cursor: pointer;">在网上找了一圈。。也没有找到相关的资料。。一点都没有。。。还有有大米公开的代码供参考。。。赶紧把学习的成果记录下来。。CM_KEY_NODE的结构：+0x014SubKeyCounts:[2]Uint4B//SubKeyCounts[0]子键的个数+0x01cSubKeyLists:[2]Uint4B//SubKeyLists[0]子键列表相差本BIN的偏移这里的subKeyList是一个偏移。。指向CM_KEY_INDEX结构。。最复杂的也是这个结构。。</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 09:26:52</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3504</span></span>  </p> </article><article class="excerpt"> <header> <a title="MySql" class="label label-important zj-del-target" href="/category/47">MySql<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/7401" title="由浅入深探究mysql索引结构原理、性能分析与优" target="_blank" onclick="return recordId('',)">由浅入深探究mysql索引结构原理、性能分析与优 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/7401" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/3.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/7401';}else{window.open('/article/7401');}" style="cursor: pointer;">http://www.phpben.com/?post=74摘要：第一部分：基础知识第二部分：MYISAM和INNODB索引结构1、简单介绍B-treeB+tree树2、MyisAM索引结构3、Annode索引结构4、MyisAM索引与InnoDB索引相比较第三部分：MYSQL优化1、表数据类型选择2、sql语句优化(1)最左前缀原则(1.1)能正确的利用索引(1.2)不能正确的利用索引(1.3)如果一个查询where子句中确实不需要password列，那</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 01:54:07</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3503</span></span>  </p> </article><article class="excerpt"> <header> <a title="Jquery" class="label label-important zj-del-target" href="/category/65">Jquery<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/12585" title="20个有创意的jQuery图片和内容滑动及弹出插件" target="_blank" onclick="return recordId('',)">20个有创意的jQuery图片和内容滑动及弹出插件 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/12585" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/16.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/12585';}else{window.open('/article/12585');}" style="cursor: pointer;">在网页的首页或图片专题页面很多地方都会用到图片滑动插件来循环切换多张图片，并且用户可以点击左右按钮来切换图片。相信大家都知道jQuery是最优秀的Javascript框架之一。以其语法简单灵活而大受Webdesigner欢迎。所以很多网页设计师结合jQuery的强大功能制作出了许多成熟的图片滑动插件，我们可以很简单地直接将这些图片滑动插件嵌入到网页中，很容易就得到了即酷又实用的jQuery图片滑动效果。1FlexSlider(Demo演示|Download</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 09:30:27</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3502</span></span>  </p> </article><div class="pagination" style="display:;"> <ul><li><a href="/search/hibernate/1/p/1">首页</a></li> <li class="prev-page"><a 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