JavaScript Promises, road to async/await - https://codingblast.com/javascript-promise-async-await

PromisesChain.js

function someFunction(value, error) {
  return new Promise((resolve, reject) => {
    if (value) {
      resolve(13);
    } else {
      reject(error);
    }
  });
}

function fetchPost(id) {
  return fetch('https://jsonplaceholder.typicode.com/posts/' + id)
  .then(
    response => response.json(), 
    error => error)
  .then(function(post) {
    return post;
  });
}

function mainFunctionSync() {
  someFunction('value').then(
    id => { 
      fetchPost(id).then(
        post => { console.log(post); },
        error => {console.error(error); }
      );
    },
    error => {
      console.error(error);
    }
  );
}

mainFunctionSync();