domain.on('error') should suppress other uncaughtException handlers

[CrabBot]

Coming from a mocha issue, I realized the following:

• domains do not "catch" errors in the sense that uncaughtException will still fire, an implementation detail probably best kept out of userland.
• In a sense, this is inconsistent with the EventEmitter API where EventEmitter.on('error') suppresses errors from being thrown, where as uncaughtException firing is a de facto failure to catch

Example:

process.on('uncaughtException', function(err) {
  console.error(err.stack)
  // Uh oh! Do as the docs recommend & bail
  process.exit()
})

var domain = require('domain').create()
domain.on('error', function(err) {
  // Proceed. We're totally cool
  console.error(err.stack)
  domain.dispose()
})
domain.run(function() {
  process.nextTick(function() {
    throw new Error('fail')
  })
})

A possible workaround would be to wrap your uncaughtException handler in a process.nextTick and then check for err.domain, but that means domains are backwards incompatible with existing uncaughtException handlers for example in 3rd party modules like mocha.

[fengmk2]

After domain.on('error') , uncaughtException event still fire doubt to what I think.

[isaacs]

Yes, we should move the default error handling function to a separate function that checks for a current domain, and emits error on it, or emits 'uncaughtException' on the process object.

[AlexeyKupershtokh]

Guys, it seems a bit off topic, but what techniqie would you recommend to re-throw errors from nested domains' error handlers to their parents' error handlers?

[isaacs]

@AlexeyKupershtokh You could do something like this:

var domain = require('domain');
var parentDomain = domain.create();
parentDomain.on('error', function(er) {
  console.error('parent got it:', er.message);
});

var myDomain = domain.create();
myDomain.on('error', function(er) {
  if (!myDomainShouldHandleThisError(er))
    parentDomain.emit('error', er);
});

myDomain.run(function() {
  setTimeout(function() {
    undefined_reference;
  });
});

function myDomainShouldHandleThisError(er) {
  // lazy kid...
  return false;
}

Output:

$ node dd.js 
parent got it: undefined_reference is not defined