Concurrent promises in JavaScript

Running many async operations at once.

const urls = ["/api/a", "/api/b", "/api/c"];

async function loadAll() {
  const requests = urls.map((url) => fetch(url));
  const responses = await Promise.all(requests);
  return Promise.all(responses.map((r) => r.json()));
}

async function loadSafely() {
  const results = await Promise.allSettled(urls.map((u) => fetch(u)));
  return results.filter((r) => r.status === "fulfilled");
}

How it works

1. Promise.all waits for every promise, failing fast.
2. Mapping over urls starts all requests immediately.
3. Promise.allSettled reports each outcome instead.

Keywords and builtins used here

• Promise
• async
• await
• const
• function
• return

The run, in numbers

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12

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Type this snippet

Step 4 of 5 in Promises, step 4 of 19 in Promises & async.

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