writable.writable
如果调用 writable.write() 是安全的，则为 true，这意味着流没有被销毁、出错或结束。
Is true if it is safe to call writable.write(), which means
the stream has not been destroyed, errored or ended.
如果调用 writable.write() 是安全的，则为 true，这意味着流没有被销毁、出错或结束。
Is true if it is safe to call writable.write(), which means
the stream has not been destroyed, errored or ended.