testasync.js

// this is our aync function
function query(x) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(x * 2)
    }, 2000)
  });
}

// First, most commonly used way long ago
function getResultOption1(cb) {
  query(1).then(res => {
    cb(res)
  })
}

getResultOption1(result => {
  console.log(result)
})

// a bit nicer, we return a promis ourselves
function getResultOption2() {
  return new Promise(resolve => {
    query(2).then(res => {
      resolve(res)
    })
  })
}

getResultOption2().then(result => {
  console.log(result)
})

// modern way using async / await
async function getResultOption3() {
  return await query(3)
}
getResultOption3().then(result => {
  console.log(result)
})