Express error handling or domain?

Question

I am building an app in nodejs and express. Can anybody help me to understand the difference between the following pieces of code:

  var app = express();
  app.use(function(err, req, res, next){
  console.error(err);
  res.render('home.ejs', {message:'Something broke!'});
  });

and

 var domain = require('domain');
 var d = domain.create();
 d.on('error', function(err) {
 console.error(err);
 res.render('home.ejs', {message:'Something broke!'});
 });

Are the two pieces of code alternative? If yes, which one is more reliable in order to avoid the app crashing on production?

Answer 1

Express wraps each function (req, res, next) {} in a try/catch. Which catches many errors, but not async errors. Domains catch async errors. However catching the error and handling it are two different things.

If you next the error (aka d.on('error', next);) it will end up in going to express error middleware, just like in your first example.

So instead of thinking about express vs domains, think try/catch vs domains. Express should be used to handle the error in either case.

Answer 2

I've managed to get async error handling working with domains with this middleware:

function(req,res,next){
    var d = domain.create();

    d.on('error',next)

    d.run(function(){
        next();
    })
}

I'm currently testing it in on my servers, but looks good for me:). I also created npm module. You can take a look at it:

npmjs.org - express-async-error

Hope this helps. :)