without_promises.js

const wait1 = (fn) => {
   setTimeout(() => {
      fn()
   }, 100)
}
const wait2 = (fn) => {
   setTimeout(() => {
      fn()
   }, 200)
}
const wait3 = (fn) => {
   setTimeout(() => {
      fn()
   }, 400)
}
wait1(() => {
   console.log("Finished wait1")
   wait2(() => {
      console.log("Finished wait2")
      wait3(() => {
         console.log("Finished wait3")
      })
   })
});