事件：'end'

¥Event: 'end'

'end' 事件来自 stream.Readable 类。'end' 事件在所有数据输出后触发，发生在 transform._flush() 中的回调被调用之后。在出现错误的情况下，不应触发 'end'。

¥The 'end' event is from the stream.Readable class. The 'end' event is emitted after all data has been output, which occurs after the callback in transform._flush() has been called. In the case of an error, 'end' should not be emitted.