Can someone please explain how every line of this code works?... Saw it during a JavaScript challenge

Question

https://code.sololearn.com/WIWrs63bakWL/?ref=app

Answer 1

isAsync = true because the program ends faster then promise executes callback.

Check out the sequence here.
https://code.sololearn.com/WzWLcf5ycZaG/?ref=app

Answer 2

Thanks a lot... I had no knowledge about promises in JavaScript