Creating async functions in JavaScript

app.js

const a = () => {
  return new Promise(resolve => {
    console.log('a')
    resolve(1)
  })
}

const b = () => {
  return new Promise(resolve => {
    console.log('b')
    setTimeout(resolve, 1000, 2)
  })
}

Promise.all([a(), b()]).then(results => console.log(results)) // a b [1, 2]