Proper error handling in node express

error.md

Proper error handling in node express

server

• Place errorHandler after all routes and before .listen
• Forget process.env.NODE_ENV
• Use knas when raising errors if you need to produce http status codes

function errorHandler(err, req, res, next) {
  // err is either obj or string
  res.status(err.status || 500).send(err.message || err); 
};

// routes here..

app.use(errorHandler);

// .listen

client

ajax

$.ajax({
  error: function(a, b, c) {
    // a.responseText is the actual error string (!) passed from the server like err.message
    // a.statusText is the http status code
    // b is a string about timeouts and parser errors
    // c is the same as a.statusText
    next(a.responseText || a.statusText);
  }
});

Ajax handlers vs http status codes

• 2XX will run successHandler
• 3xx - 5xx will run errorHandler

Relevant http status codes

• 400 bad request (from client)
• 401 unauthorized
• 404 not found
• 500 internal server error