Express.js 4 and domain module: why domain doesn't handle the error?

Question

I'm trying to familiarize myself with domain module. So, I created a study sample below:

var express = require('express')
var domain = require('domain')
var supertest = require('supertest')

describe('some', function() {
    it('some', function(done) {
      var app = express()
      app.use(function(req, res, next) {
        var d = domain.create();
        d.on('error', function(e) {
          console.log('here')
        });
        d.run(next)
      })
      app.use('*', function(req, res) {
        throw new Error()
        res.end()
      })
      supertest(app).get('/').expect(200, done)
    })
})

But, it doesn't work as I expected. Can somebody explain why it never reaches error callback?

Additional info:

$ npm list --depth=0
├── express@4.13.4
├── mocha@2.4.5
└── supertest@1.2.0
$ node -v
v6.0.0

P.S.: it's deprecated, I know. But on the moment there is no alternatives and large codebase of projects which actually use it

https://nodejs.org/api/domain.html says "This module is pending deprecation", so it is something that will be replaced with new API. — gevorg, May 11 '16 at 15:18
Yes, there might be no good alternative. Sure it depends on problem that you are trying to solve with module. What for you need it? — gevorg, May 11 '16 at 15:26
it's a little bit out of scope of the question. I have a project which actually uses `domain` module — kharandziuk, May 11 '16 at 15:27

score 2 · Accepted Answer · edited Sep 17 '17 at 14:18

2

The reason is that Express 4 is doing exception handling before your code with domain works, you can make sure that I am correct by adding following handler on bottom, it kinda wraps everything in try/catch and if there is no error handler prints error stack:

app.use(function (err, req, res, next) {
   console.log(err);
   res.end();
});

edited Sep 17 '17 at 14:18

GilZ

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answered May 11 '16 at 16:12

gevorg

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actually it's quite interesting that nobody notice before that middleware for error handling(based on domain) doesn't work in our project:) – kharandziuk May 11 '16 at 16:27
yep, that happens, it might work on previous Express versions :) – gevorg May 11 '16 at 16:27

Express.js 4 and domain module: why domain doesn't handle the error?

1 Answers1