promise waterfall from collection

promiseWaterfall.js

function promiseWaterfall(callbacks) {
  var first = callbacks[0]();
  return callbacks.slice(1).reduce(function (accumulator, callback) {
    return accumulator.then(callback)
  }, first)
}

var collection = [{id:'A'},{id:'B'},{id:'C'},{id:'D'}];

var promiseArray = collection.map(function(obj) {
  return function fn() {
   return new Promise(function(resolve, reject) {
    setTimeout(function() {
      console.log('### '+ obj.id + ' ' + new Date().getSeconds());
      resolve(obj);
    }, 1000);
   }); 
});

promiseWaterfall(promiseArray)
  .then(function (result) {
    console.log(result)
});

// jsbin: http://jsbin.com/jazuku/edit?js,console
// output
//"### A 1"
//"### B 2"
//"### C 3"
//"### D 4"