zlib.ZlibBase

class zlib.ZlibBase extends undefined

Not exported by the node:zlib module. It is documented here because it is the base class of the compressor/decompressor classes.

This class inherits from stream.Transform, allowing node:zlib objects to be used in pipes and similar stream operations.

The zlib.bytesWritten property specifies the number of bytes written to the engine, before the bytes are processed (compressed or decompressed, as appropriate for the derived class).

zlib.close(callback?): void

Close the underlying handle.

zlib.flush(kind?, callback): void

• kind Default: zlib.constants.Z_FULL_FLUSH for zlib-based streams, zlib.constants.BROTLI_OPERATION_FLUSH for Brotli-based streams, and zlib.constants.ZSTD_e_flush for Zstd-based streams.
• callback Function

Flush pending data. Don't call this frivolously, premature flushes negatively impact the effectiveness of the compression algorithm.

Calling this only flushes data from the internal zlib state, and does not perform flushing of any kind on the streams level. Rather, it behaves like a normal call to .write(), i.e. it will be queued up behind other pending writes and will only produce output when data is being read from the stream.

zlib.params(level, strategy, callback): void

This function is only available for zlib-based streams, i.e. not Brotli.

Dynamically update the compression level and compression strategy. Only applicable to deflate algorithm.

zlib.reset(): void

For inflate and deflate streams, reset the compressor/decompressor to factory defaults.

For Brotli streams, start a new compression or decompression session while preserving the configured parameters and dictionary.

For Zstd streams, cancel the current frame and start a new session while preserving the configured parameters and dictionary. If pledgedSrcSize was configured for a Zstd compressor, it applies again to the next frame.

Resetting a gzip stream after it has emitted output for an incomplete member causes the stream to error with ERR_ZLIB_INCOMPLETE_FRAME. Resetting at that point would discard the member state while the bytes already written out remain at the start of the output stream, leaving it undecodable. Call .end(), or start over with a new gzip stream, instead. zlib-wrapped deflate may still reset() after a flush; callers that reuse the compressor discard the first output. Raw deflate has no wrapper header, so reset() after a flush still concatenates.

Calling reset() while a write is in progress throws an Error.

Resetting an incomplete Zstd compression frame after it has emitted output causes the stream to error with ERR_ZLIB_INCOMPLETE_FRAME. Resetting at that point would discard the frame state while the bytes already written out remain at the start of the output stream, leaving it undecodable. Call .end(), or start over with a new stream, instead.