Even though promise is supposed to solve the callback hell problem,
for this particular challenge,
we can defer resolving the main Promise
until the last batch of data is retrieved
by making promise inside a promise (recursively).
<pre class="shiki github-dark shaku"><code>function throttlePromises(funcs, max){ let result = []; if (!funcs || !funcs.length) return Promise.resolve(result); // Called recursively, executing "max" API calls per batch const createBatch = (batchId, resolve, reject) =&gt; { const startIdx = batchId * max; const endIdx = startIdx + max; const batchedPromises = funcs.slice(startIdx, endIdx).map(fn =&gt; fn()); Promise.all(batchedPromises) .then(batchedData =&gt; { result.push(...batchedData); if (result.length === funcs.length) { resolve(result); } else { createBatch(batchId+1, resolve, reject); } }) .catch(err =&gt; reject(err)); }; return new Promise((res, rej) =&gt; createBatch(0, res, rej));}</code></pre>

Easy batching with... callback hell :)

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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, …