if (exchanged) break;
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.
，详情可参考同城约会
这就是当下中国一些富人所起的表率，开创害礼坏俗的先例而不自知。
if (stack.length 0) {