Lesson 19 — Promise.all

Wait for many at once

Promise.all([p1, p2, …]) starts from several Promises and gives one Promise that resolves to an array of all results. The results come back in the same order as you passed them, even if a later one finishes first. If any one fails, the whole thing fails.

const [a, b] = await Promise.all([fetchUser(), fetchPosts()]);

Why it matters: loading three things in parallel takes as long as the slowest one, not the sum of all three.