How Async Await behaves in loops

async-await-loop.js

// our cool promise of future; serialize promises
function future(val){ 
  console.log("lala ", val);
  return new Promise((resolve, reject) => {
     setTimeout(resolve, 2000, val);
  })
}

//1. await waits in this case
(async () => { 
  for (i in [1,2,3,4]) { 
    const x = await future(i); 
    console.log(x) 
  } 
  console.log('done') 
})()

/*
lala  0
Promise {<pending>}
0
lala  1
1
lala  2
2
lala  3
3
done
*/

//2. await won't wait in this case; fire and forget
(() => { 
  [1,2,3,4].forEach(async i => { 
    let x = await future(i); 
    console.log('-> ', x) 
  }); 
  console.log("done") 
})()

/*
lala  1
lala  2
lala  3
lala  4
done
undefined
->  1
->  2
->  3
->  4
*/

// 3.make use of inherent parallelism
(() => {
  Promise.all([1,2,3,4].map(i => future(i)))
     .then(result => result.forEach(x => console.log('-> ', x)));
  console.log("done") 
})()

/*
lala  1
lala  2
lala  3
lala  4
done
undefined
->  1
->  2
->  3
->  4
*/