title: Uncaught TypeError: Cannot call method 'appendChild' of null?
body: <p>I.m using pagedown editor in my project.</p>
  
  <p>My HTML code:</p>
  
  <pre><code>&lt;script src="&lt;?php echo base_url('assets/js/Markdown.Converter.js')?&gt;"&gt;&lt;/script&gt;
  &lt;script src="&lt;?php echo base_url('assets/js/Markdown.Sanitizer.js')?&gt;"&gt;&lt;/script&gt;
  &lt;script src="&lt;?php echo base_url('assets/js/Markdown.Editor.js')?&gt;"&gt;&lt;/script&gt;
  
  
  &lt;div style="padding-top:20px;" class="control-group"&gt;
                          &lt;div class="controls"&gt;
                              &lt;textarea class="wmd-input" id="wmd-input"&gt;&lt;/textarea&gt;
                          &lt;/div&gt;
                  &lt;/div&gt;
                  &lt;div style="padding-top:20px;" class="control-group"&gt;
                      &lt;label for="signature" class="control-label user-label"&gt;学校专业&lt;/label&gt;
                          &lt;div class="controls"&gt;
                              &lt;div id="wmd-preview" class="wmd-panel wmd-preview"&gt;&lt;/div&gt;
                          &lt;/div&gt;
                  &lt;/div&gt;
  </code></pre>
  
  <p>and my javascript code:</p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
  $(function() 
          {
              var converter1 = Markdown.getSanitizingConverter();
              var editor1 = new Markdown.Editor(converter1);
              editor1.run();
          });
  &lt;/script&gt;
  </code></pre>
  
  <p>google chrome browser throw out an error "Uncaught TypeError: Cannot call method 'appendChild' of null ?", what's wrong in my code?</p>
  
  <p>PS: appendChild is in the file of Markdown.Editor.js:1332</p>