Q promise array reduce example based on http://stackoverflow.com/a/17764496/3753772

reduceq.js

var Q = require("q");

var arr = [1,2,3,4];

arr.reduce(function(prev, item) {
  return prev.then(function(p) {
    console.log(item);
    return Q.delay(0);
  });
}, Q.resolve(1));