In production web applications, firing hundreds of concurrent HTTP requests simultaneously can overwhelm browser network pools or hit API rate limits. Building an Async Concurrency Limiter (Task Pool) is a classic senior live coding interview task.
Problem Statement
Write a function mapConcurrent(items, limit, asyncFn) that executes asyncFn for every item in items, ensuring at most limit promises execute concurrently.
Optimal Solution
JAVASCRIPT
Pairlet Snippet
async function mapConcurrent(items, limit, asyncFn) {
const results = [];
const executing = new Set();
for (const [index, item] of items.entries()) {
const p = Promise.resolve().then(() => asyncFn(item, index));
results[index] = p;
executing.add(p);
const clean = () => executing.delete(p);
p.then(clean, clean);
if (executing.size >= limit) {
await Promise.race(executing);
}
}
return Promise.all(results);
}Try this Problem Live on Pairlet
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