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Debug Stream

Transform stream for debugging stream pipelines.

Installation

npm install @stdlib/streams-node-debug

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

vardebugStream=require('@stdlib/streams-node-debug');

debugStream( [options,] [clbk] )

Creates a transform stream for debugging stream pipelines.

varENV=require('@stdlib/process-env');// Set the `DEBUG` environment variable...ENV.DEBUG='*';varstream=debugStream({'name': 'my-stream'});stream.write('a');stream.write('b');stream.write('c');stream.end();

The function accepts the following options:

• name: debug namespace.
• objectMode: specifies whether a stream should operate in objectMode. Default: false.
• highWaterMark: specifies the Buffer level at which write() calls start returning false.
• allowHalfOpen: specifies whether a stream should remain open even if one side ends. Default: false.
• readableObjectMode: specifies whether the readable side should be in objectMode. Default: false.

To set streamoptions,

varopts={'name': 'my-app','objectMode': true,'highWaterMark': 64,'allowHalfOpen': true,'readableObjectMode': false// overridden by `objectMode` option when `objectMode=true`};varstream=debugStream(opts);

By default, each chunk is logged as a JSON stringified string, along with the chunk index. For more control over logging behavior, provide a callback.

functionlogger(debug,chunk,idx){debug('Received a new chunk...');debug('Beep: %s',chunk.beep);debug('Boop: %s',chunk.boop);}varopts={'name': 'my-pipeline'};varstream=debugStream(opts,logger);

debugStream.factory( [options] )

Returns a function for creating streams which are identically configured according to provided options.

varopts={'objectMode': true,'highWaterMark': 64};varfactory=debugStream.factory(opts);

This method accepts the same options as debugStream(), except for name, which must be provided explicitly.

factory( name[, clbk] )

Creates a debug stream.

varfactory=debugStream.factory();varstreams=[];vari;// Assign each stream to a separate debug namespace...for(i=0;i<10;i++){streams.push(factory('stream '+i));}

debugStream.objectMode( [options,] [clbk] )

This method is a convenience function to create streams which always operate in objectMode.

varstream=debugStream.objectMode({'name': 'beep-boop'});stream.write({'value': 'a'});stream.write({'value': 'b'});stream.write({'value': 'c'});stream.end();

This method accepts the same options as debugStream(); however, the method will always override the objectMode option in options.

Notes

• If the DEBUG environment variable is not set, no data is logged.
• Providing a name option is strongly encouraged, as the DEBUG environment variable can be used to filter debuggers.

Examples

varparseJSON=require('@stdlib/utils-parse-json');varstdout=require('@stdlib/streams-node-stdout');vartransformFactory=require('@stdlib/streams-node-transform').factory;vardebug=require('@stdlib/streams-node-debug').objectMode;functionparse(chunk,enc,clbk){clbk(null,parseJSON(chunk));}functionpluck(chunk,enc,clbk){clbk(null,chunk.value);}functionsquare(chunk,enc,clbk){varv=+chunk;clbk(null,v*v);}functiontoStr(chunk,enc,clbk){clbk(null,chunk.toString());}functionjoin(chunk,enc,clbk){clbk(null,chunk+'\n');}// Create a factory for generating streams running in `objectMode`:vartStream=transformFactory({'objectMode': true});// Create streams for each transform:vars1=tStream(parse);vard1=debug({'name': 'parse'});vars2=tStream(pluck);vard2=debug({'name': 'pluck'});vars3=tStream(square);vard3=debug({'name': 'square'});vars4=tStream(toStr);vard4=debug({'name': 'toString'});vars5=tStream(join);vard5=debug({'name': 'join'});// Create the pipeline:s1.pipe(d1).pipe(s2).pipe(d2).pipe(s3).pipe(d3).pipe(s4).pipe(d4).pipe(s5).pipe(d5).pipe(stdout);// Write data to the pipeline...varv;vari;for(i=0;i<100;i++){v='{"value":'+i+'}';s1.write(v,'utf8');}s1.end();

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See Also

• @stdlib/streams-node/debug-sink: writable stream for debugging stream pipelines.
• @stdlib/streams-node/inspect: transform stream for inspecting streamed data.

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Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.