promiseSerial.js

/*
 * promiseSerial resolves Promises sequentially.
 * @example
 * const urls = ['/url1', '/url2', '/url3']
 * const funcs = urls.map(url => () => $.ajax(url))
 *
 * promiseSerial(funcs)
 *   .then(console.log)
 *   .catch(console.error)
 */
const promiseSerial = funcs =>
  funcs.reduce((promise, func) =>
    promise.then(result => func().then(Array.prototype.concat.bind(result))),
    Promise.resolve([]))

// some url's to resolve
const urls = ['/url1', '/url2', '/url3']

// convert each url to a function that returns a promise
const funcs = urls.map(url => () => $.ajax(url))

// execute Promises in serial
promiseSerial(funcs)
  .then(console.log.bind(console))
  .catch(console.error.bind(console))

Oops. Updated! Thanks!