Promise API

new Promise()

• new Promise((resolve, reject) => {})

const getDinosaur = (name) => {
  return new Promise((resolve, reject) => {
    resolve({name})
  })
}

//Shorthand for synchronous values as a Promise
const getDinosaur = (name) => Promise.resolve({name})
const getDinosaur = (name) => Promise.reject(new Error("Dinosaurs went extinct!")

Promise.then

• Get the asynchronous value

getDinosaur("Stegosaurus")
  .then((dinosaur) => console.log(dinosaur))

• .then() coerces all returned values to a Promise (chaining)

getDinosaur("Brontosaurus")
  .then((dinosaur) => dinosaur.name)
  .then((name) => console.log(name))

Promise.catch

• Handle errors with a Promise

const getDinosaurs = () => Promise.reject("Connection Timed Out!")
getDinosaurs()
  .catch((reason) => console.error(reason))

Promise.all

• Asynchronous iteration

const getDinosaur = (name) =>
  new Promise((resolve) =>
    setTimeout(() =>
      resolve({name, age: jurrasicPeriod()}),
      Math.random() * 3000)
  )
const jurrasicPeriod = () => Math.floor(Math.random() * 54e6) + 145e6
const log = (value) => console.log(value)
const dinosaurs = ['Brontosaurus', 'Tyrannosaurus', 'Stegosaurus']

Promise.all(dinosaurs.map(getDinosaur))
  .then(log) //-> [{name: "Brontosaurus", age: ...}, {name: "Tyrannosaurus", age: ...}, {name: "Stegosaurus", age: ...}]