Medium Promise.race Examples

Promise-race.js

// Example 1:
const dog = new Promise((resolve, reject) => {
  setTimeout(() => resolve('🐶'), 1000)
})
const cat = new Promise((resolve, reject) => {
  setTimeout(() => resolve('🐈'), 2000)
})

Promise.race([dog, cat]).then((value) => {
// value will be the resolved value of 
// first promise which resolved.
  console.log(value) // '🐶'
})

// Example 2:
const bear = new Promise((resolve, reject) => {
  setTimeout(() => reject('🐻'), 1000)
})
const panda = new Promise((resolve, reject) => {
  setTimeout(() => resolve('🐼'), 2000)
})

Promise.race([bear, panda])
  .then((value) => {
    console.log(value)
  })
  .catch((error) => {
  // value will be the rejected value of 
  // first promise which was rejected.
    console.error(error) // 🐻
  })

// Practical Usage:
// Here Promise will throw 'request timeout' 
// if the api call takes more than 30 seconds
Promise.race([
    fetch('/endpoint'),
    new Promise(function (resolve, reject) {
      setTimeout(() => 
        reject(new Error('request timeout')), 30000)
    })
]).then(response => console.log(response))
.catch(error => console.log(error))