Promise.first

async-await.ts

async function first<T>(promises: Promise<T>[]): Promise<T> {
	const rejections: any[] = [];

	for (const promise of promises) {
		try {
			return await promise;
		}
		catch (reason) {
			rejections.push(reason);
		}
	}

	throw rejections;
}

recursive.ts

function first<T>(promises: Promise<T>[]): Promise<T> {
	return first_rec(promises, []);
}

function first_rec<T>(promises: Promise<T>[], previousRejections: any[]): Promise<T> {
	if (promises.length === 0) {
		return Promise.reject(previousRejections);
	}

	const [head, ...tail] = promises;
	return head.catch(reason => first_rec(tail, previousRejections.concat(reason)));
}