asynchronous progreamming

//Top to bottom (code read)

//Instant (synchronous)
//Not Instant (asynchronous)
// API call
// setTimeOut (our own)
//file reading/file write , database data store, data fetch

//asynchronous code dealing
//callback
//promise
//Async await

// function getOne() {
//   return 1
// }

// function getTwo() {
//   return 2
// }

// function getThree(callback) {
//   setTimeout(() => {
//     callback(3)
//   }, 2000)
// }

// function getFour(number) {
//   return number
// }

// console.log(getOne())
// console.log(getTwo())


//   getThree(function (data) {
//     console.log(data) //result is available
//     //getFour()
//    // console.log(getFour(data + 1))  //Dependency
//   })

// console.log(getFour())

//promise pattern
function getOne() {
  return 1
}

function getTwo() {
  return 2
}

function getThree(isResolved) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      if (isResolved) {
        resolve(3)
      } else {
        reject(new Error(3))
      }
    }, 2000)
  })
}

function getFour(number) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve(number)
    }, 2000)
  })
}

console.log(getOne())
console.log(getTwo())
// console.log(getThree())

getThree(true)
  .then(data => {
    console.log(data)
    return getFour(data + 1)
    // .then(fourData => console.log(fourData))
    // .catch(err => console.log(err))
    // console.log(getFour(data + 1))
  })
  .then(data => console.log(data))
  .catch(err => console.log(err))

// console.log(getFour(4))

//callback hell(nesting callback)

//Async await uses promise (Behind the scene)

//fetch

// fetch('https://jsonplaceholder.typicode.com/todos')
//   .then(res => res.json())
//   .then(data => console.log(data))
//   .catch(err => console.log(err))

async function init() {
  try {
    const todos = await (
      await fetch('https://jsonplaceholder.typicode.com/todos')
    ).json()
    // const todos = await res.json()
    return todos
  } catch (err) {
    console.log(err)
  }
}

;(async function () {
  console.log(await init())
})()