• callback <Function> 当剩余的数据被 flush 后的回调函数。

该函数不能被应用程序代码直接调用。 它应该由子类实现,且只能被内部的 Readable 类的方法调用。

某些情况下,转换操作可能需要在流的末尾发送一些额外的数据。 例如,zlib 压缩流时会储存一些用于优化输出的内部状态。 当流结束时,这些额外的数据需要被 flush 才算完成压缩。

自定义的转换流transform._flush() 方法是可选的。 当没有更多数据要被消费时,就会调用这个方法,但如果是在 'end' 事件被触发之前调用则会发出可读流结束的信号。

transform._flush() 的实现中,readable.push() 可能会被调用零次或多次。 当 flush 操作完成时,必须调用 callback 函数。

transform._flush() 方法有下划线前缀,因为它是在定义在类的内部,不应该被用户程序直接调用。

  • callback <Function> A callback function (optionally with an error argument and data) to be called when remaining data has been flushed.

This function MUST NOT be called by application code directly. It should be implemented by child classes, and called by the internal Readable class methods only.

In some cases, a transform operation may need to emit an additional bit of data at the end of the stream. For example, a zlib compression stream will store an amount of internal state used to optimally compress the output. When the stream ends, however, that additional data needs to be flushed so that the compressed data will be complete.

Custom Transform implementations may implement the transform._flush() method. This will be called when there is no more written data to be consumed, but before the 'end' event is emitted signaling the end of the Readable stream.

Within the transform._flush() implementation, the readable.push() method may be called zero or more times, as appropriate. The callback function must be called when the flush operation is complete.

The transform._flush() method is prefixed with an underscore because it is internal to the class that defines it, and should never be called directly by user programs.