Using a generator to trigger a sequence of promises

promise-generator-trigger.js

function* triggerGen(res, rej) {
  const result = yield;
  if (result) {
    res(result);
  } else {
    rej();
  }
}
var trigger;

const prom = new Promise((res, rej) => {
    trigger = triggerGen(res, rej);
    trigger.next();
});


prom
  .then(function(x) {
    console.log(x);
    return Promise.resolve(x * 2)
  })
  .then(function(y) {
    console.log(y);
    return Promise.resolve(y * 2);
  })
  .then(function(z) {
    console.log(z * 2);
  });

setTimeout(function(){
    trigger.next(2);
},1);