promise.js

const Types = Object.freeze({
  Unit: Symbol('Unit')
});

function uselessPromise() {
  return new Promise(resolve => {
    console.log('Doing stuff !!!');
    setTimeout(() => resolve(Types.Unit), 200)
  }).then(res => {
    if (res === Types.Unit && 
        res !== 'unit' && 
        res !== Symbol('unit')) {
      return 'Success !!!';
    } else {
      return 'Failure :(';
    }
  });
}

uselessPromise()
  .then(res => console.log('Result is : ', res));