code: function(handler, error, error_message) {
      if(typeof handler === 'function') {
          handler(error, error_message);
      } else {
          console.error(error_message || 'Unhandled exception raised: ', error);
      }
  }
docs: If an error handler function is given, it is called with the error instance, otherwise log the error to the console
  with a possible custom error message prefix. The custom message is passed also the error handler.
  
  @param {function} handler - The error handler function.
  @param {object | Error} error - The error instance.
  @param {string} [error_message] - The custom error message, optional.