For newbies you may experience warning catch by chrome developer tool that you might take few hours to resolve it and hard to find reason behind why it happened when using ReactJS. Code level seems to be nothing wrong with extremely simple code.
Warning: React.createElement: type should not be null, undefined, boolean, or number. It should be a string (for DOM elements) or a ReactClass (for composite components).
Root Caused: System throw warning and not displaying “Hello, world! I am a CommentList” due to CommentList component load after CommentBox component.
Resolution: Just move CommentList component script before CommentBox will resolve this warning.