pLimit for modern Node

pLimit.ts

export function pLimit(concurrency: number) {
    let running = 0;

    let resolves: (() => void)[] = [];

    return async <T>(fn: () => Promise<T>): Promise<T> => {
        if (running >= concurrency) {
            await new Promise<void>((resolve) => {
                resolves.push(resolve);
            });
        }

        running++;

        return (async () => {
            try {
                return await fn();
            } finally {
                running--;

                resolves[0]?.();

                resolves.shift();
            }
        })();
    };
}