promise-pls.js

// The function
function subscribe(promises, cb) {
  let result = Array.from({ length: promises.length }).fill(null);

  promises.forEach((promise, index) => {
    promise.then(val => {
      const clonedResult = [...result];
      clonedResult[index] = val;
      cb(clonedResult);
      result = clonedResult;
    });
  });
}

// Usage
subscribe([
  new Promise(resolve => setTimeout(() => resolve(2), 2000)),
  new Promise(resolve => setTimeout(() => resolve({ pizza: true }), 1000)),
], (stuff) => {
  console.log('hi', stuff);
})