One of the example how to use promise (with async code) in javascript

Javascript Promise

=========WITHOUT PROMISE====================

console.log('Request data...')

setTimeout(() => {
  console.log('Preparing data...')
  const backendData = {
    server: 'aws',
    port: 2000,
    status: 'working'
  }
  
 setTimeput(() => {
   backendData.modified = true
   console.log('Data received', backendData)
 }, 2000)
}, 2000)

=========WITH PROMISE====================

const promise = new Promise(function(resolve, reject) {
  setTimeout(() => {
    console.log('Preparing data...')
    const backendData = {
      server: 'aws',
      port: 2000,
      status: 'working'
    }
    resolve()
  },2000)
})

promise.then(data => {
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        data.midfied = true
        resolve(data) //reject(data)
      }, 2000}
    })
    // promiseSecond.then(clientData => {
    //   console.log('Data received', clientData)
    // })
  })
===========how to handle errors============
  .then(clienData => {
    clientData.fromPromise = true
    return cleintData
  })
  .then(data => {
    console.log('Modified', data)
  })
  .catch(err => console.error('Error:', err))
============FINALLY always exectued===========
  .finally(() => console.log('Finally'))


=========SLEEP===============
const sleep(() => {
  return new Promise (resolve => {
    setTimeput(() => resolve(), ms)
  })
}

// sleep(2000).then(() => console.log('After 2 sec'))
// sleep(3000).then(() => console.log('After 3 sec'))

=============WAIT for several methods====================

Promise.all([sleep(2000), sleep(5000)]).then(() => {
  console.log('All promises')
})  

=============TO SEE what was executed first===========

Promise.race([sleep(2000), sleep(5000)]).then(() => {
  console.log('All promises')
})