// 测试用例（验证你的代码正确性，可自行删除/保留）
* @param left 左边界
。关于这个话题，safew官方下载提供了深入分析
Web streams has no synchronous path. Even if your source has data ready and your transform is a pure function, you still pay for promise creation and microtask scheduling on every operation. Promises are fantastic for cases in which waiting is actually necessary, but they aren't always necessary. The new API lets you stay in sync-land when that's what you need.
She is now facing calls to pause a government plan to scrap the lower minimum wage for 16 and 17 year olds, as some employers are saying it will make it too expensive to hire young people.