callback-count 
Count callbacks before continuing, tiny control flow helper, allows dynamic counting.
Flow control
var callbackCount = require('callback-count');
var counter = callbackCount(done);
setTimeout(counter.inc().next, 100);
setTimeout(counter.inc().next, 100);
function done (err) {
console.log('finished.');
}.inc() allows you to dynamically update the number of callbacks you are expecting.
var callbackCount = require('callback-count');
var counter = callbackCount(done);
counter.inc().inc().inc();
counter.next().next().next();
function done (err) {
console.log('finished.');
}The constructor can take an initial value for the count expected
var callbackCount = require('callback-count');
var counter = callbackCount(3, done);
counter.next().next().next();
function done (err) {
console.log('finished.');
}.next() decrements the count and callsback when the count has reached 0
var counter = createCounter(3, done);
counter.next().next().next();
function done (err) {
console.log(counter.count); // 0
console.log('finished.');
}if .next() receives an error it will callback immediately
var counter = createCounter(3, done);
counter.next(new Error('boom'));
function done (err) {
console.log(err.message); // boom
}