execute promises in series

promise-series.js

// Promise returning functions to execute
function doFirstThing(){ return Promise.resolve(1); }  
function doSecondThing(res){ return Promise.resolve(res + 1); }  
function doThirdThing(res){ return Promise.resolve(res + 2); }  
function lastThing(res){ console.log("result:", res); }

var fnlist = [ doFirstThing, doSecondThing, doThirdThing, lastThing];

// Execute a list of Promise return functions in series
function pseries(list) {  
  var p = Promise.resolve();
  return list.reduce(function(pacc, fn) {
    return pacc = pacc.then(fn);
  }, p);
}

pseries(fnlist);  
// result: 4

Source:
http://www.datchley.name/promise-patterns-anti-patterns/

Don't forget to pass promise factories not promises.
I.e.: This won't work:

pseries(promise1(), promise2(), ...])

Whereas this will:

pseries(promise1, promise2, ...])

Also:
https://pouchdb.com/2015/05/18/we-have-a-problem-with-promises.html