Javascript Promise tips

After using Promise for a while, I realized the followings might be good to know:

• The executor function of a promise is executed immediately after creation. That means if you create a Promise object using new, the function you passed in (the executor) will run right after the new statement. ¹
  For example, in the following codes:

  var prom = new Promise((resolve, reject) => {
  console.log('1')
  setTimeout(() => {
    resolve('3')
  }, 3000)
  })
  prom.then(console.log)
  console.log('2')
  

The output is:

1
2
3