Race promises into settled values with concurrency limit

_raceAllSettled.js

async function* raceAllSettled (iterable, concurrency = 4) {
    const executing = new Set();

    const consume = async () => {
        const value = await Promise.race(executing);

        executing.delete(value.promise);
        delete value.promise;

        return value;
    };

    for (const item of iterable) {
        const promise = promised(item).then(
            (value) => ({ status: 'fulfilled', value, promise }),
            (reason) => ({ status: 'rejected', reason, promise }),
        );

        executing.add(promise);

        if (executing.size >= concurrency) {
            yield await consume();
        }
    }

    while (executing.size) {
        yield await consume();
    }
}

const promised = (value) => {
    return (value && value.then) ? value : Promise.resolve(value);
}

demo.js

const promises = [
  new Promise((resolve) => setTimeout(resolve, 1000, 456)),
  123,
  Promise.resolve(234),
  Promise.reject(345),
];

for await (const value of raceAllSettled(promises)) {
  console.log(value);
}

// > { status: 'fulfilled', value: 123 }
// > { status: 'fulfilled', value: 234 }
// > { status: 'rejected', value: 345 }
// > { status: 'fulfilled', value: 456 }