Asynchronous in JavaScript

async-await.js

function randomInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1) + min)
}

const saveToCloud = () => {
  return new Promise((resolve, reject) => {
    const delay = randomInt(500, 3000)

    setTimeout(() => {
      resolve('Save to cloud success in ' + delay + 'ms')
      // reject() 
    }, delay)

  })
}

const sendNotification = () => {
  return new Promise((resolve, reject) => {
    const delay = randomInt(500, 3000)

    setTimeout(() => {
      resolve('Send notification success in ' + delay + 'ms')
      // reject() 
    }, delay)

  })
}

const fetchNews = () => {
  return new Promise((resolve, reject) => {
    const delay = randomInt(500, 3000)

    setTimeout(() => {
      resolve('Fetch new data success in ' + delay + 'ms')
      // reject()
    }, delay)

  })
}

(async () => {
  console.log(await saveToCloud())
  console.log(await sendNotification())
  console.log(await fetchNews())
})()

callback-hell.js

const request = require('request')

request('url1', function (err, res, body) {
  request('url2', function (err2, res2, body2) {
    request('url3', function (err3, res3, body3) {
      request('url4', function (err4, res4, body4) {
        request('url5', function (err5, res5, body5) {
          request('url6', function (err6, res6, body6) {
            request('url7', function (err7, res7, body7) {
              request('url8', function (err8, res8, body8) {
                request('url9', function (err9, res9, body9) {
                  request('url10', function (err10, res10, body10) {
                    request('url11', function (err11, res11, body11) {
                      request('url12', function (err12, res12, body12) {
                        // Actual code
                      })
                    })
                  })
                })
              })
            })
          })
        })
      })
    })
  })
})

callback.js

function randomInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1) + min)
}

function saveToCloud(callback) {
  const delay = randomInt(500, 3000)
  setTimeout(() => {
    if (typeof callback === 'function') {
      callback()
    }
    console.log('Data has been saved to cloud service in ' + delay + 'ms')
  }, delay)
}

function sendNotification(callback) {
  const delay = randomInt(500, 3000)
  setTimeout(() => {
    if (typeof callback === 'function') {
      callback()
    }
    console.log('Notification has been sent in ' + delay + 'ms')
  }, delay)
}

function fetchNews(callback) {
  const delay = randomInt(500, 3000)
  setTimeout(() => {
    if (typeof callback === 'function') {
      callback()
    }
    console.log('Latest news has been fetched in ' + delay + 'ms')
  }, delay)
}

saveToCloud()
sendNotification()
fetchNews()

// saveToCloud(function () {
//   sendNotification(function () {
//     fetchNews(() => {
//       
//     })
//   })
// })

promise-demo.js

function randomInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1) + min)
}

const saveToCloud = () => {
  return new Promise((resolve, reject) => {
    const delay = randomInt(500, 3000)

    setTimeout(() => {
      resolve('Save to cloud success in ' + delay + 'ms')
      // reject()
    }, delay)

  })
}

const sendNotification = () => {
  return new Promise((resolve, reject) => {
    const delay = randomInt(500, 3000)

    setTimeout(() => {
      resolve('Send notification success in ' + delay + 'ms')
      // reject()
    }, delay)

  })
}

const fetchNews = () => {
  return new Promise((resolve, reject) => {
    const delay = randomInt(500, 3000)

    setTimeout(() => {
      resolve('Fetch new data success in ' + delay + 'ms')
      // reject()
    }, delay)

  })
}

// ------------------------------------------
// Get promise result
// ------------------------------------------

// const result = saveToCloud()
// result
//   .then(message => {
//     console.log(message)
//   })
//   .catch(err => {
//     throw new Error('Fail')
//   })


// ------------------------------------------
// Dependents
// ------------------------------------------

// saveToCloud()
//   .then(messageFromSaveToCloud => {
//     console.log(messageFromSaveToCloud)
//     return sendNotification()
//   })
//   .then(messageFromSendNotification => {
//     console.log(messageFromSendNotification)
//     return fetchNews()
//   })
//   .then(messageFromFetchNews => {
//     console.log(messageFromFetchNews)
//   })
//   .catch(err => {
//     throw new Error('Fail')
//   })


// ------------------------------------------
// Promise.all - All promises must resolved
// ------------------------------------------

// const result = Promise.all([
//   saveToCloud(),
//   sendNotification(),
//   fetchNews(),
// ])

// result.then(([a, b, c]) => {
//   console.log(a)
//   console.log(b)
//   console.log(c)
// }).catch(err => {
//   throw new Error('Fail')
// })


// ------------------------------------------
// Promise.race - Who's the winner?
// ------------------------------------------

// const result = Promise.race([
//   saveToCloud(),
//   sendNotification(),
//   fetchNews(),
// ])

// result.then(winner => {
//   console.log(winner)
// }).catch(err => {
//   throw new Error('Fail')
// })