regularPlusone.ts

// ----- Without async ----- //
function regularPlusOne (i: number): Promise<number> {
  return new Promise(resolve => {
    resolve(i + 1)
  })
}

// ----- With async ----- //
async function plusOne (i: number): Promise<number> {
  return i + 1
}

// Both functions can be used as 
plusOne(1)
.then(plusOne)
.then(plusOne)
.then(console.log) // outputs 4
.catch(console.error)