The `flat` function allows you to write then-able functions without explicitly creating your own Promises, and instead receiving the promise resolution/rejection functions as a destructure-able object as a first argument.

flat.js

function flat(fn) {
  return function (...args) {
    return new Promise((resolve, reject) => {
      fn.call(this, {resolve, reject}, ...args);
    });
  };
}

index.js

(async function () {
  const a = x => new Promise(resolve => resolve(x));
  const b = flat(({resolve}, x) => resolve(x));
  const results = Promise.all([a('👌'), b('💯')]);
  console.log(await results);
  // > ["👌", "💯"]
})();

return function (...args) {
  return new Promise((resolve, reject) => {
    fn.call(this, {resolve, reject}, ...args);
  });
}