race promises

race.js

const invertPromise = (promise) => new Promise(
  (resolve, reject) => promise.then(reject, resolve)
)

const raceToSuccess = (promises) => invertPromise(
  Promise.all(promises.map(invertPromise))
)

const fast = () => {
  return new Promise((resolve) => {
    setTimeout(() => {
      resolve('fast')
    }, 750)
  })
}

const slow = () => {
  return new Promise((resolve) => {
    setTimeout(() => {
      resolve('slow')
    }, 3000)
  })
}

async function main () {
  const promises = [fast(), slow()]

  const first = await raceToSuccess(promises)

  console.log('first was', first)
}

main()