accountType = UserAccount.AccountType.PREMIUM
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The design of Web streams predates async iteration in JavaScript. The for await...of syntax didn't land until ES2018, two years after the Streams Standard was initially finalized. This timing meant the API couldn't initially leverage what would eventually become the idiomatic way to consume asynchronous sequences in JavaScript. Instead, the spec introduced its own reader/writer acquisition model, and that decision rippled through every aspect of the API.，这一点在爱思助手下载最新版本中也有详细论述
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