Node: async.foreach fails silently when error is uncaught exception is thrown

Question

Node: async.foreach fails silently when error is uncaught exception is thrown

I'm wrapping some async executed 'child'-functions in an async.forEach construct (from the great lib: https://github.com/caolan/async)

When one of these child-functions fails with an uncaught exception the entire node-process hangs. (since a callback is never returned to the async.forEach construct, async.forEach still thinks a child-function is busy)

However I would have thought at least the thrown exception would bubble up, since I'm not catching it anywhere. Is there a way to configure how async.forEach handles these exceptions? It's really hard programming against this.

node.js
asynchronous
error-handling
promise

Answer 1

Solved. For future reference:

OK so I basically had this:

var async = require("async");
var cb = function(){
   //denote done to async.foreach
}
async.forEach(defaultFunctions,function(defaultFunc,cb){   
  defaultFunc(cb);
},callback);

The problem was that when a certain defaultFunction throws an uncaught exception, the exception is swallowed by async.forEach. Moreover there's no way to catch it in the calling context.

The result is severe: complete halt of the parent node-process, without any trance what's causing it.

In the called context (i.e: the defaultFunction that throws the exception) I could of course meticulously try to catch all exceptions, but these functions are hot-pluggable, possibly ranging in the hundreds in the end and I don't want to burden each of these functions with 100% full-proof error-handling.

A solution I've found is to use promises (using the Q library -> github.com/kriskowal/q ) to wrap the functions in:

var async = require("async")
var Q = require("q");
var cb = function(){
   //denote done to async.foreach
}
async.forEach(defaultFunctions,function(defaultFunc,cb){   
  var obj = {
    defaultFunc: defaultFunc
  } 
  return Q.ncall(obj.defaultFunc,obj)
    .then(function(result){
       return cb() ;
    }fail(function(err){
       return cb(err); //ANY thrown uncaught error in obj.defaultFunc will get 
                       //caught and changed to a correct callback as needed
                       //for async.forEach
    }
},callback);

Of course, now I realize async.foreach can be done trivially with Q.promises instead but that's another story...