await-perf.js

(function() {
  'use strict'

  async function pending() {
    return 11
  }

  function mayPending() {
    if (Math.random() < 0.001) {
       return pending()
    }
    return 22
  }

  async function main() {
    console.time('s1')
    for (let i = 0; i < 1e6; i++) {
      const val = await mayPending()
    }
    console.timeEnd('s1')


    console.time('s2')
    for (let i = 0; i < 1e6; i++) {
      const ret = mayPending()
      const val = ret.then ? await ret : ret
    }
    console.timeEnd('s2')
  }

  main()
})()

s1: 2412.416015625 ms
s2: 20.87890625 ms