'end' 事件

'end' 事件来自 stream.Readable 类。 'end' 事件在所有数据输出后触发，该事件发生在调用 transform._flush() 中的回调之后。 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.