限制数量的并发请求

function batchFetch(urls: string[], max: number) {
	if (urls.length === 0) {
		return Promise.resolve([]);
	}
	if (max <= 0) {
		return Promise.reject(new Error('max must be greater than 0'));
	}
	const p = new Promise<unknown[]>((resolve) => {
		const result: unknown[] = [];
		let currentIndex = 0;
		let runningCount = 0;
		let finishedCount = 0;
		function _run() {
			const id = currentIndex;
			if (runningCount >= max || id >= urls.length) {
				return;
			}
			const url = urls[currentIndex];
			currentIndex++;
			runningCount++;

			fetch(url)
				.then((response) => {
					result[id] = response;
				})
				.catch((error) => {
					result[id] = error;
				})
				.finally(() => {
					runningCount--;
					finishedCount++;
					if (finishedCount === urls.length) {
						resolve(result);
						return;
					}
					_run();
				});
		}

		for (let i = 0; i < Math.min(max, urls.length); i++) {
			_run();
		}
	});

	return p;
}