JSON stringify an Error in Express

express_error_json.js

// development error handler
// will print stacktrace

if (app.get('env') === 'development') {
  app.use(function(err, req, res, next) {
    res.status(err.status || 500);

    function err2JSON (err) {
      var obj = JSON.parse(
        JSON.stringify(err, Object.getOwnPropertyNames(err))
      );

      if (obj.stack) {
        obj.stack = obj.stack.split('\n');
      }

      return obj;
    }

    res.json({
      ret: -1,
      msg: err.message,
      err: err2JSON(err)
    });
  });
}