Promise sleep

hello.js

function wait () {
  return new Promise((resolve, reject) => {
    setTimeout(resolve, 1000)
  })
}

function foo (i) {
  return new Promise((resolve, reject) => {
    console.log(i)
    resolve()
  })
}

let promise = Promise.resolve()

for (let i = 1; i <= 3; i++) {
  if (i >= 2) {
    promise = promise.then(() => wait())
  }
  promise = promise.then(() => foo(i))
}