Two ways to find out when all your async stuff is done

gistfile1.js

// Imagine that this is somebody else's async tool that you're using
var doAsyncThing = function(thing, cb) {
	cb(thing + '!')
}

// So you have this utility function
var callThisWhenTheThingsAreDone = function(callback, number_of_things_to_do) {
	var things_done = 0
	return function() {
		things_done++
		if (number_of_things_to_do === things_done) {
			callback()
		}
	}
}

// And this is the thing that happens once all the async stuff is done
var finisher = function() {
	console.log("ALL DONE!")
}

// So, you can just do this
var things_to_work_on = ['what', 'what', 'in', 'the', 'butt']
var thingFinished = callThisWhenTheThingsAreDone(finisher, things_to_work_on.length)


things_to_work_on.forEach(function(thing) {
	doAsyncThing(thing, function(result) {
		console.log("I got back " + result)
		thingFinished()
	})
})

gistfile2.js

var doAsyncThing = function(thing, cb) {
  cb(thing + '!')
}

var finisher = function() {
	console.log("ALL DONE!")
}

var things_to_work_on = ['what', 'what', 'in', 'the', 'butt']
var things_done = 0

things_to_work_on.forEach(function(thing) {
	doAsyncThing(thing, function(result) {
		console.log("I got back " + result)
		things_done++
		if (things_done === things_to_work_on.length) {
			finisher()
		}
	})
})