Any difference between await Promise.all() and multiple await?

Note:

This answer just covers the timing differences between await in series and Promise.all. Be sure to read @mikep's comprehensive answer that also covers the more important differences in error handling.

For the purposes of this answer I will be using some example methods:

• res(ms) is a function that takes an integer of milliseconds and returns a promise that resolves after that many milliseconds.
• rej(ms) is a function that takes an integer of milliseconds and returns a promise that rejects after that many milliseconds.

Calling res starts the timer. Using Promise.all to wait for a handful of delays will resolve after all the delays have finished, but remember they execute at the same time:

const data = await Promise.all([res(3000), res(2000), res(1000)])//                              ^^^^^^^^^  ^^^^^^^^^  ^^^^^^^^^//                               delay 1    delay 2    delay 3//// ms ------1---------2---------3// =============================O delay 1// ===================O           delay 2// =========O                     delay 3//// =============================O Promise.all

async function example() {  const start = Date.now()  let i = 0  function res(n) {    const id = ++i    return new Promise((resolve, reject) => {      setTimeout(() => {        resolve()        console.log(`res #${id} called after ${n} milliseconds`, Date.now() - start)      }, n)    })  }  const data = await Promise.all([res(3000), res(2000), res(1000)])  console.log(`Promise.all finished`, Date.now() - start)}example()