案例：Extjs案例     状态：可编辑再运行    进入竖版
 运行结果　
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<!DOCTYPE html>
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<html>
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   <head>
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   <link href="//cdn.bootcss.com/extjs/6.2.0/classic/theme-classic/resources/theme-classic-all.css" rel="stylesheet" />
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   <script type="text/javascript" src="//cdn.bootcss.com/extjs/6.2.0/ext-all.js"></script>
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      <script type="text/javascript">
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         Ext.onReady(function(){
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            Ext.create('Ext.Button', {
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               renderTo: Ext.getElementById('helloWorldPanel'),
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               text: 'My Button',
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               listeners: {
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                  click: function() {
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                     Ext.MessageBox.alert('Alert box', 'Button is clicked');
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                  }
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               }
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            });
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         });
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      </script>
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   </head>
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   <body>
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      <p> Please click the button to see event listener </p>
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      <div id = 'helloWorldPanel' />   <!--  panel will be rendered here-- >
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   </body>
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</html>