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.
if url in self.seen_urls:
，这一点在heLLoword翻译官方下载中也有详细论述
Москвичи пожаловались на зловонную квартиру-свалку с телами животных и тараканами18:04
Darren Connor, 55, appeared on Friday at Manchester magistrates court, where he denied possession of an offensive weapon in a public place without lawful authority or reasonable excuse.