Asked by Arjun Rao · 751 views · 3 replies
I want to save some items and then log "all done":
items.forEach(async (item) => {
await saveItem(item);
});
console.log("all done");"all done" prints first, before any of the saves finish. I put await right there, so why is it not waiting?
The await is waiting, but only inside each callback. forEach calls your async function, gets a promise back, and throws that promise away. It never waits on it, so the loop ends straight away and console.log runs.
Pick based on what you want.
One at a time, in order: use for...of, where await pauses the loop itself:
for (const item of items) {
await saveItem(item);
}
console.log("all done");All at once: map to promises and wait for all of them:
await Promise.all(items.map((item) => saveItem(item)));
console.log("all done");The second is faster, but if any save rejects, Promise.all rejects straight away. The other saves keep running; you just stop waiting for them. Use Promise.allSettled if you need every result regardless.
Worth saying: "all at once" with 5,000 items means 5,000 requests at the same moment, and most APIs will rate-limit you for that. For big lists, process them in chunks of, say, 20 with Promise.all per chunk.