runPromisesInSeries - 运行连续的 promises

运行连续的 promise。

使用 Array.reduce() 通过创建 promise 链来运行连续的 promises，其中每个 promise 在 resolved 时返回下一个 promise 。

const runPromisesInSeries = ps => ps.reduce((p, next) => p.then(next), Promise.resolve());

const delay = d => new Promise(r => setTimeout(r, d));
runPromisesInSeries([() => delay(1000), () => delay(2000)]); // Executes each promise sequentially, taking a total of 3 seconds to complete