promises.js

function pipeline(fs, val, done) {
  if (fs.length === 0) done(null, val)
  else                 fs[0](val, function(err, val) {
                         if (err)  done(err)
                         else      pipeline(fs.slice(1), val, done)
                       })
}

pipeline([
  asyncFunctionOne,
  function(val, next){ next(somethingSync(val)) },
  asyncFunctionTwo,
  function(_, next){ next(somethingElseSync()) },
  asyncFunctionThree,
], null, function(err, val) {
  console.log('Done')
})

/* Without Promises */
asynchronousFunctionOne(function(value){
	somethingSync(value);
	asynchronousFunctionTwo(function(){
		somethingElseSync();
		asynchronousFunctionThree(function(){
			console.log("Done!");
		});
	});
});

/* With Promises */
Promise.try(function(){
	return asynchronousFunctionOne();
}).then(function(value){
	somethingSync(value);
	return asynchronousFunctionTwo();
}).then(function(){
	somethingElseSync();
	return asynchronousFunctionThree();
}).then(function(){
	console.log("Done!");
});