p-limit 7.3.1: Cap how many async tasks run at once with p-limit

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import pLimit from 'p-limit';

// pLimit returns a function that queues calls past the limit. The tasks must
// be wrapped BEFORE Promise.all sees them: Promise.all(tasks.map(t => t()))
// starts everything at once and the limiter never applies.
export async function runLimited(tasks, concurrency) {
  const limit = pLimit(concurrency);
  return Promise.all(tasks.map((task) => limit(task)));
}

import { strict as assert } from 'node:assert';
import { runLimited } from '../src/index.mjs';

let active = 0;
let peak = 0;
const task = (i) => async () => {
  active += 1;
  peak = Math.max(peak, active);
  await new Promise((r) => setTimeout(r, 20));
  active -= 1;
  return i;
};

const results = await runLimited([0, 1, 2, 3, 4, 5].map(task), 2);

assert.deepEqual(results, [0, 1, 2, 3, 4, 5]);
assert.equal(peak, 2, `peak concurrency was ${peak}, expected the limit of 2`);
assert.equal(active, 0);
console.log('CONTRACT PASS: p-limit held concurrency at 2 and preserved result order');