promise-chaining-and-await-examples.js

function a() {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log('a')
      resolve()
    }, 1000)
  })
}

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

// Promise chaining.
a()
  .then(() => {
    return b()
  })
  .then(() => {
    return a()
  })
  .then(() => {
    return b()
  })
  .then(() => console.log('done'))

// Compact example of Promise chaining. The return is implied and you don't have to use curly braces (also true when doing Array.map/reduce/etc).
a()
  .then(() => b())
  .then(() => a())
  .then(() => b())
  .then(() => console.log('done'))

// Using async/await.
async function go() {
  await b()
  await a()
  await b()
  console.log('done')
}
go()