实现可写流

stream.Writable 类被扩展以实现 Writable 流。

自定义的 Writable 流必须调用 new stream.Writable([options]) 构造函数并实现 writable._write() 和/或 writable._writev() 方法。

The stream.Writable class is extended to implement a Writable stream.

Custom Writable streams must call the new stream.Writable([options]) constructor and implement the writable._write() and/or writable._writev() method.