Promise.all

Start several tasks together and wait until every one finishes.

Promise.all([p1, p2, p3]) runs work in parallel and fulfills with an array of results in the same order. Wall-clock time is about the longest delay — not the sum. If any promise rejects, the whole Promise.all rejects (one fail fails all).

Results

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Timing

—

Compare parallel Promise.all with awaiting one after another.

Important JavaScript

const a = delayValue("Ava", 400);
const b = delayValue("Ben", 700);
const c = delayValue("Cara", 500);

Promise.all([a, b, c])
  .then(function (names) {
    // ["Ava", "Ben", "Cara"] — wall time ≈ 700ms, not 1600ms
    console.log(names);
  })
  .catch(function (error) {
    // If any one rejects, you land here
    console.log(error.message);
  });