<pre><code>function throttlePromises(funcs, max) {
  const iterator = funcs[Symbol.iterator]();

  const result = [];

  let worker = async () =&gt; {
    for (const func of iterator) {
      const data = await func();
      result.push(data);
    }
  };

  let workers = [];
  while (max-- &gt; 0) {
    workers.push(worker());
  }

  return Promise.all(workers).then(() =&gt; result);
}

</code></pre>

Practice Symbol.iterator

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Say you need to fetch some data through 100 APIs, and as soon as possible. If you use Promise.all(), 100 requests go to your server at the same time, …