prints 1,2,3,4,5, 6 using promises at different times

promise.js

p1 = function(r) {

  console.log(new Date(), r);
  
  p2 = new Promise(r => setTimeout(x => r(3), 3000));
  p3 = new Promise(r => setTimeout(x => r(4), 7000));
  p4 = new Promise(r => setTimeout(x => r(5), 2000));
  
  s  = Promise.resolve();
  s2 = s.then(x => p2);
  s3 = s2.then(v => console.log(new Date(), v));
  s4 = s3.then(x => p3 );
  s5 = s4.then(v => console.log(new Date(), v));
  s6 = s5.then(x => p4 );
  s7 = s6.then(v => console.log(new Date(), v));

  return s7;
};

p = new Promise(r => setTimeout(x => r(2), 1000));
z = p.then(p1);
z.then(x => console.log(new Date(), 6));
console.log(new Date(), 1)

see https://gist.github.com/ernestlv/a22eb8cafbff0a2f0561cb5ec4d7df38