// see https://stackoverflow.com/a/24985483

const fetchList = list => {
  return list.reduce((promise, item) => {
    return promise.then(() => {
      // or any other promise
      return new Promise((resolve) => {
        console.log(`delay for ${item} secs`);
        setTimeout(() => {
          resolve();
        }, item * 1000);
      });
    });
  }, Promise.resolve());
};

const listDelays = '123456'.split('').map(() => Math.round( Math.random() * 10 ) + 1);

fetchList(listDelays).then(() => console.log('job 1 finished'));

// 2nd method
function asyncMethod() {
  return new Promise((resolve) => {
    setTimeout(() => {
      console.log('item done');
      resolve();
    }, 3000);
  });
}

let chain = Promise.resolve();

const asyncArray = '123'.split('').map(() => asyncMethod);

for(const func of asyncArray) {
  chain = chain.then(func);
}

chain.then(() => console.log('job 2 finished'));