promise-mapSeries-without-bluebird.js

const rp = require('request-promise');
const urls = ['https://jsonplaceholder.typicode.com/todos/1', 'https://jsonplaceholder.typicode.com/todos/2'];

const newUrls = urls.map(url => () => rp(url));

Promise.resolve()
    .then(x => newUrls[0]())
    .then(x => newUrls[1]());

console.log(newUrls);

Promise.resolve([])
  .then(all => {
    return newUrls[0]().then(result => all.concat(result));
  })
  .then(all => {
    return newUrls[1]().then(result => all.concat(result));
  });

// const rrr = [];
// Promise.resolve(rrr)
//     .then(x => newUrls[0]().then(Array.prototype.concat.bind(x)))
//     .then(x => newUrls[1]().then(Array.prototype.concat.bind(x)))
//     .then(result => console.log(result))


const promiseSerial = newUrls => 
    newUrls.reduce((acc, newUrl) => {
    console.log(acc);
    return Promise.resolve(acc).then(x => newUrl().then(Array.prototype.concat.bind(x)))
    }, Promise.resolve([]));
      
promiseSerial(newUrls).then(result => console.log(result));