SOURCE

let p1 = Promise.resolve(10),
    p2 = Promise.resolve(20),
    p3 = Promise.resolve(30);
console.log(typeof p1);
Promise.map = function(values, cb) {
  return Promise.all(values.map(function(e) {
    return new Promise(function(resolve, reject) {
      cb(e, resolve);
    });
  }));
}

Promise.map([p1, p2, p3], function(p, cb) {
  p.then(function(value) {
    cb(value + 10);
  })
}).then(function(value) {
  console.log(value[0]);
})