Difference of using async / await vs promises?

async/await and promises are closely related. async functions return promises, and await is syntactic sugar for waiting for a promise to be resolved.

The only drawback from having a mix of promises and async functions might be readability and maintainability of the code, but you can certainly use the return value of async functions as promises as well as await for regular functions that return a promise.

Whether you choose one vs the other mostly depends on availability (does your node.js / browser support async?) and on your aesthetic preference, but a good rule of thumb (based on my own preference at the time of writing) could be:

If you need to run asynchronous code in series: consider using async/await:

return asyncFunction()
.then(result => f1(result))
.then(result2 => f2(result2));

vs

const result = await asyncFunction();
const result2 = await f1(result);
return await f2(result2);

If you need nested promises: use async/await:

return asyncFunction()
.then(result => {
  return f1(result)
  .then(result2 => f2(result, result2);
})

vs

const result = await asyncFunction();
const result2 = await f1(result);
return await f2(result, result2);

If you need to run it in parallel: use promises.

return Promise.all(arrayOfIDs.map(id => asyncFn(id)))

It has been suggested you can use await within an expression to await multiple tasks like so:
*note, this still awaits in sequence from left to right, which is OK if you don’t expect errors. Otherwise the behaviour is different due to fail fast behaviour of Promise.all()

const [r1, r2, r3] = [await task1, await task2, await task3];

(async function() {
  function t1(t) {
    console.time(`task ${t}`);
    console.log(`start task ${t}`);
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        console.timeEnd(`task ${t}`);
        resolve();
      }, t);
    })
  }

  console.log('Create Promises');
  const task1 = t1(100);
  const task2 = t1(200);
  const task3 = t1(10);

  console.log('Await for each task');
  const [r1, r2, r3] = [await task1, await task2, await task3];

  console.log('Done');
}())

But as with Promise.all, the parallel promises need to be properly handled in case of an error. You can read more about that here.

Be careful not to confuse the previous code with the following:

let [r1, r2] = [await t1(100), await t2(200)];

function t1(t) {
  console.time(`task ${t}`);
  console.log(`start task ${t}`);
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.timeEnd(`task ${t}`);
      resolve();
    }, t);
  })
}
console.log('Promise');
Promise.all([t1(100), t1(200), t1(10)]).then(async() => {

  console.log('Await');
  let [r1, r2, r3] = [await t1(100), await t1(200), await t1(10)]
});

Using these two methods is not equivalent. Read more about the difference.

In the end, Promise.all is a cleaner approach that scales better to an arbitrary number of tasks.