promises.js

const wait1 = (fn) => {
   return new Promise(resolve => setTimeout(resolve, 100))
}
const wait2 = (fn) => {
   return new Promise(resolve => setTimeout(resolve, 200))
}
const wait3 = (fn) => {
   return new Promise(resolve => setTimeout(resolve, 300))
}
wait1()
   .then(wait2)
   .then(wait3)
   .then(function() {
      console.log("All good!");
   });