anchor.diff:        {'sender': 'frame', 'type': 'stdout', 'message': message.toString()}, '*');
     }
   }
  +// Unload previous version.
  +require.undef('dartpad_main');
   ''';
   
       /// The javascript exception handling for Dartpad catches both errors
  
positive.code: 
    String _decorateJavaScript(String javaScript, {String modulesBaseUrl}) {
      final String postMessagePrint = '''
  const testKey = '$testKey';
  
  function dartPrint(message) {
    if (message.startsWith(testKey)) {
  
negative.code:     String javaScript, {
      String modulesBaseUrl,
    }) {
      return _send('execute', {
        'html': html,
        'css': css,
        'js': _decorateJavaScript(javaScript, modulesBaseUrl: modulesBaseUrl),
      });
    }
  
  