title: React Tutorial - Cannot read property 'toString' of undefined
body: <p>I need to learn React in the next day and started with the official tutorial. All is good until I get to this state of my code where I am getting an error and am not sure how to get around it:</p>
  
  <pre><code>&lt;/head&gt;
      &lt;body&gt;
      &lt;div id="content"&gt;&lt;/div&gt;
       &lt;!-- script type="text/babel" src="scripts/example.js"&gt;&lt;/script --&gt;
       &lt;script type="text/babel"&gt;
         var CommentBox = React.createClass( {
            render: function() {
              return (
                &lt;div className = "commentBox"&gt;
                  &lt;h1&gt;Comments&lt;/h1&gt;
                  &lt;CommentList /&gt;
                  &lt;CommentForm /&gt;
                  &lt;Comment /&gt;
                &lt;/div&gt;
                );
           }
         });
  
            var CommentList = React.createClass({
              render: function () {
                return (
                 &lt;div className = "commentList"&gt;
                    &lt;Comment author = "Michael Johnson"&gt;This is one 
                        comment&lt;/Comment&gt;
                    &lt;Comment author = "Daniel Kammer"&gt;This is the 'second' 
                        comment&lt;/Comment&gt;
                    &lt;/div&gt;
                 );
              }
            });
  
             var CommentForm = React.createClass({
              render: function () {
                return (
                  &lt;div className = "commentForm"&gt;
                     Hello, world! I am a CommentForm.
                  &lt;/div&gt;
                  );
              }
            });
  
            var Comment = React.createClass({
             var md = new Remarkable();
             render: function () {
            return (
              &lt;div className = "comment"&gt;
                &lt;h2 className = "commentAuthor"&gt;
                  {this.props.author}
                &lt;/h2&gt;
              *** ERROR IS GENERATED BY THE BELOW STATEMENT ***
                  {md.render(this.props.children.toString())}
              &lt;/div&gt;
              );
          }
        });
  </code></pre>
  
  <p>The rest of the tutorial continues forward with the md.render statement - so I need to understand how to resolve this error</p>