12-promise.ts

// PromisedNumber :: () -> Promise<error>
const PromisedNumber = () => new Promise(function (fulfill, reject) {
  setTimeout(() => { reject(new Error('could not produce number')) }, 500)
})
// PromisedString :: () -> Promise<string>
const PromisedString = () => new Promise(function (fulfill, reject) {
  setTimeout(() => { fulfill(10) }, 1000)
})

console.log('start')

const AsyncPipeline = () => {
  // we don't actually need these two variables
  const promisedNumber = PromisedNumber()
  const promisedString = PromisedString()

  promisedNumber.then((value) => {
    console.log('number: ', value)
    return promisedString
  })
  .then((value) => { console.log('string:', value) })
  .catch((err) => { console.log('error:', err.message) })
}

AsyncPipeline()

console.log('finish')