Support for node js domains

[mkeshavgarg]

promise.js breaks node js domains.

//express.js
domain = require('domain');
app.use(function(req, res, next) {
    var reqDomain = domain.create();

    reqDomain.run( function (req, res, next) {
        console.log(process.domain);     //defined

        Promise.all([promise1, promise2]).then(function() {
            console.log(process.domain);    //  ERROR: process.domain is undefined
        }) 
    })
})

[ForbesLindesay]

If you want to use domains you need to do require('promise/domains') instead of require('promise'). You shouldn't really need domains when using promises though, since promises handle error bubbling properly anyway.

[edef1c]

It's also worth noting that domains are deprecated (https://nodejs.org/api/domain.html#domain_domain)

[ForbesLindesay]

Yes, that too. I never understood why anyone thought they were a good idea. I guess it was just people who didn't understand promises.

[mkeshavgarg]

I am not using domains for error bubbling.

I am aware that domains will soon be fully deprecated and will be replaced by some other API but for now my use case needs node.js domains.

In java there is a concept called thread local which helps to define variables in the context of that thread but in node we do not have anything like that but domains.
I found domains very useful in providing context for particular set of operations and mimicking thread local storage.

Use Case:

1. I need to access the request context in mongoose model pre/post hooks
2. I need to access the request context in request handlers

Solution: Create domain in the context of request

app.use(function(req, res, next) {
    var reqDomain = domain.create();
    reqDomain.run(next);
});

Now with the use of process.domain, I will be able to access 'data' bound to above created domain anywhere
Eg:

var d = process.domain
d.obj = {};

Similar use case has been discussed here:
nodejs/node-v0.x-archive#3733

[ForbesLindesay]

You can easily implement this yourself on top of promises via something like:

var Promise = require('promise');
var originalThen = Promise.prototype.then;
Promise.prototype.then = function (cb, eb) {
  if (typeof cb === 'function') {
    // bind cb to the current domain
  }
  if (typeof eb === 'function') {
    // bind eb to the current domain
  }
  return originalThen.call(this, cb, eb);
};

We're not going to provide it by default because it represents a huge performance hit.