Flat-Chained Promise Example

flatChainedPromiseExample.js

function asyncFunction(bool) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      if(bool) {
        resolve('Promise resolved after .5 of a second');
      } else {
        reject('Promise rejected after .5 of a second');
      }
    }, 500);   
  });
}

// Promise flat-chain to avoid nesting
// FYI: returning a function call that 
// returns a Promise in a .then will pass 
// the unresolved promise down to the next
// .then in the chain, and the callback function
// in the next .then will only run once the passed
// promise has resolved. 
// (this can be done with synchronous values too(data other than Promises))
asyncFunction(true).then(result => asyncFunction(result))
                   .then(secondResult => asyncFunction(secondResult))
                   .then(thirdResult => asyncFunction(thirdResult))
                   .then(fourthResult => {
                      console.log('Reached the end of the promise flat-chain: ', fourthResult);
                   })
                   .catch(err => {
                      console.log(`If any Promise in the chain fails/rejects, 
                                   the rejected Promise will bubble/pass 
                                   it's result to this .catch: `, err);
                   });