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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">3535</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/13860" title="AChartEngine应用之LineChart（模拟动态生命特" target="_blank" onclick="return recordId('',)">AChartEngine应用之LineChart（模拟动态生命特 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/13860" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/7.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/13860';}else{window.open('/article/13860');}" style="cursor: pointer;">AChartEngine应用之LineChart（模拟动态生命特征值图）接着上一次写的内容，构建动态曲线图，并产生与用户交互，考虑到数据都是活动的，不可能总是用静态数据，所以我下面的demo就是模拟。项目作用：模拟生命特征值图，动态显示分钟脉搏生命特征值走向每隔1000ms产生50组数据，并填充到表格中，主要使用的到是Handler+Task，因为我是用Activity显示这个表格每次产生的数据都需要快速的填充到主线程UI中，所以我就用Handler，这里</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 22:08:56</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3535</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/11358" title="股票API之---新浪财经频道" target="_blank" onclick="return recordId('',)">股票API之---新浪财经频道 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/11358" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/4.jpg" alt="" title=""></a> </div> <span class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/11358';}else{window.open('/article/11358');}" style="cursor: pointer;">实时股票数据接口大全股票数据的获取目前有如下两种方法可以获取:1.http/javascript接口取数据2.web-service接口1.http/javascript接口取数据1.1Sina股票数据接口以大秦铁路（股票代码：601006）为例，如果要获取它的最新行情，只需访问新浪的股票数据接口：http://hq.sinajs.cn/list=sh601006这个url会返回一串文本，例如：varhq_str_sh601006="大秦铁路,27.55,</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 09:29:42</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3535</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/26239" title="Python math库 ln(x)运算的实现及原理" target="_blank" onclick="return recordId('',)">Python math库 ln(x)运算的实现及原理 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/26239" 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/26239';}else{window.open('/article/26239');}" style="cursor: pointer;">这个是很有用的一个运算，除了本身可以求自然对数，还是求指数函数需要用到的基础函数。实现原理就是泰勒展开，最简单是在x=1处进行泰勒展开：但该函数离1越远越难收敛，同时大于2时无法收敛，所以需要进行换元，然后重新展开：但是该换元在接近0时或者接近无穷大时收敛困难，处在1到10范围内收敛快且精度高，所以对大于10或小于1的值进行分解如下：ln(55000)=ln(5.5)+4ln10ln(0.0015)=ln(1.5)-4ln10ln10为算好的值，可直接由l</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 17:50:16</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3534</span></span>  </p> </article><article class="excerpt"> <header> <a title="CSS" class="label label-important zj-del-target" href="/category/68">CSS<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/2512" title="图解div+css命名规则" target="_blank" onclick="return recordId('',)">图解div+css命名规则 </a> </h2> </header> <div class="focus"> <a class="zj-del-target" href="/article/2512" 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/2512';}else{window.open('/article/2512');}" style="cursor: pointer;">一个好的命名习惯对一个网页制作人员来说可以提高代码修改的效率及代码的可读性，本图是彦磊根据自己的习惯整理而成，希望和大家交流，每个人的习惯不一样，不一下完全按照这样的规则来但一定要有自己的一套规则。图解div+css命名规则</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 01:32:57</span></span> <span class="muted"><i class="fa fa-eye"></i><span class="zj-icon-text">3534</span></span>  </p> </article><div class="pagination" style="display:;"> <ul><li><a href="/search/form/1/p/1">首页</a></li> <li class="prev-page"><a href="/search/form/1/p/185">上一页</a></li> <li><a href="/search/form/1/p/184">184</a></li><li><a href="/search/form/1/p/185">185</a></li><li 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