Run tasks with a concurrency limit

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The async question that most people get almost right, and the ordering detail that catches them.

The question

Write pool(tasks, limit) where tasks is an array of functions returning promises.

Run at most limit at a time and resolve with the results in the original order.

If one rejects, the others should still finish and you should report which failed.

const tasks = urls.map(u => () => fetch(u).then(r => r.json()));
const results = await pool(tasks, 5);

// results[i] corresponds to tasks[i]
// [{ status: "fulfilled", value }, { status: "rejected", reason }, ...]

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The worked solution

written by a person · not a grade

Score yourself

0 of 5 marked

Workers rather than batches, with the reason30
Results in original order20
A rejection does not abort the rest, and is reported25
Explained why tasks must be functions15
Handled limit > length and empty input10

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