https://github.com/stdlib-js/streams-node-debug
Transform stream for debugging stream pipelines.
https://github.com/stdlib-js/streams-node-debug
debug inspect javascript log monitor node node-js nodejs readable spy stdlib stream streams tap transform util utilities utility utils writable
Last synced: about 1 month ago
JSON representation
Transform stream for debugging stream pipelines.
- Host: GitHub
- URL: https://github.com/stdlib-js/streams-node-debug
- Owner: stdlib-js
- License: apache-2.0
- Created: 2021-06-15T17:47:13.000Z (almost 5 years ago)
- Default Branch: main
- Last Pushed: 2026-03-16T04:59:26.000Z (about 2 months ago)
- Last Synced: 2026-03-16T14:13:47.248Z (about 2 months ago)
- Topics: debug, inspect, javascript, log, monitor, node, node-js, nodejs, readable, spy, stdlib, stream, streams, tap, transform, util, utilities, utility, utils, writable
- Language: JavaScript
- Homepage: https://github.com/stdlib-js/stdlib
- Size: 1.52 MB
- Stars: 3
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
- Citation: CITATION.cff
- Security: SECURITY.md
- Notice: NOTICE
Awesome Lists containing this project
README
About stdlib...
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The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.
When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.
To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!
# Debug Stream
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
> [Transform stream][transform-stream] for [debugging][node-debug] stream pipelines.
## Installation
```bash
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][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).
- If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).
- For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).
The [branches.md][branches-url] 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
```javascript
var debugStream = require( '@stdlib/streams-node-debug' );
```
#### debugStream( \[options,] \[clbk] )
Creates a [transform stream][transform-stream] for [debugging][node-debug] stream pipelines.
```javascript
var ENV = require( '@stdlib/process-env' );
// Set the `DEBUG` environment variable...
ENV.DEBUG = '*';
var stream = debugStream({
'name': 'my-stream'
});
stream.write( 'a' );
stream.write( 'b' );
stream.write( 'c' );
stream.end();
```
The function accepts the following `options`:
- **name**: [debug][node-debug] namespace.
- **objectMode**: specifies whether a [stream][stream] should operate in [objectMode][object-mode]. Default: `false`.
- **highWaterMark**: specifies the `Buffer` level at which `write()` calls start returning `false`.
- **allowHalfOpen**: specifies whether a [stream][stream] should remain open even if one side ends. Default: `false`.
- **readableObjectMode**: specifies whether the readable side should be in [objectMode][object-mode]. Default: `false`.
To set [stream][stream] `options`,
```javascript
var opts = {
'name': 'my-app',
'objectMode': true,
'highWaterMark': 64,
'allowHalfOpen': true,
'readableObjectMode': false // overridden by `objectMode` option when `objectMode=true`
};
var stream = 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`.
```javascript
function logger( debug, chunk, idx ) {
debug( 'Received a new chunk...' );
debug( 'Beep: %s', chunk.beep );
debug( 'Boop: %s', chunk.boop );
}
var opts = {
'name': 'my-pipeline'
};
var stream = debugStream( opts, logger );
```
#### debugStream.factory( \[options] )
Returns a `function` for creating [streams][transform-stream] which are identically configured according to provided `options`.
```javascript
var opts = {
'objectMode': true,
'highWaterMark': 64
};
var factory = debugStream.factory( opts );
```
This method accepts the same `options` as [`debugStream()`](#debug-stream), **except** for `name`, which must be provided **explicitly**.
##### factory( name\[, clbk] )
Creates a [debug][node-debug] stream.
```javascript
var factory = debugStream.factory();
var streams = [];
var i;
// 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][stream] which **always** operate in [objectMode][object-mode].
```javascript
var stream = 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()`](#debug-stream); however, the method will **always** override the [objectMode][object-mode] option in `options`.
## Notes
- If the [`DEBUG`][node-debug] environment variable is **not** set, no data is logged.
- Providing a `name` option is **strongly** encouraged, as the [`DEBUG`][node-debug] environment variable can be used to filter debuggers.
## Examples
```javascript
var parseJSON = require( '@stdlib/utils-parse-json' );
var stdout = require( '@stdlib/streams-node-stdout' );
var transformFactory = require( '@stdlib/streams-node-transform' ).factory;
var debug = require( '@stdlib/streams-node-debug' ).objectMode;
function parse( chunk, enc, clbk ) {
clbk( null, parseJSON( chunk ) );
}
function pluck( chunk, enc, clbk ) {
clbk( null, chunk.value );
}
function square( chunk, enc, clbk ) {
var v = +chunk;
clbk( null, v*v );
}
function toStr( chunk, enc, clbk ) {
clbk( null, chunk.toString() );
}
function join( chunk, enc, clbk ) {
clbk( null, chunk+'\n' );
}
// Create a factory for generating streams running in `objectMode`:
var tStream = transformFactory({
'objectMode': true
});
// Create streams for each transform:
var s1 = tStream( parse );
var d1 = debug({
'name': 'parse'
});
var s2 = tStream( pluck );
var d2 = debug({
'name': 'pluck'
});
var s3 = tStream( square );
var d3 = debug({
'name': 'square'
});
var s4 = tStream( toStr );
var d4 = debug({
'name': 'toString'
});
var s5 = tStream( join );
var d5 = 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...
var v;
var i;
for ( i = 0; i < 100; i++ ) {
v = '{"value":'+i+'}';
s1.write( v, 'utf8' );
}
s1.end();
```
* * *
## See Also
- [`@stdlib/streams-node/debug-sink`][@stdlib/streams/node/debug-sink]: writable stream for debugging stream pipelines.
- [`@stdlib/streams-node/inspect`][@stdlib/streams/node/inspect]: transform stream for inspecting streamed data.
* * *
## Notice
This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib].
#### Community
[![Chat][chat-image]][chat-url]
---
## License
See [LICENSE][stdlib-license].
## Copyright
Copyright © 2016-2026. The Stdlib [Authors][stdlib-authors].
[npm-image]: http://img.shields.io/npm/v/@stdlib/streams-node-debug.svg
[npm-url]: https://npmjs.org/package/@stdlib/streams-node-debug
[test-image]: https://github.com/stdlib-js/streams-node-debug/actions/workflows/test.yml/badge.svg?branch=main
[test-url]: https://github.com/stdlib-js/streams-node-debug/actions/workflows/test.yml?query=branch:main
[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/streams-node-debug/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/streams-node-debug?branch=main
[chat-image]: https://img.shields.io/badge/zulip-join_chat-brightgreen.svg
[chat-url]: https://stdlib.zulipchat.com
[stdlib]: https://github.com/stdlib-js/stdlib
[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors
[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules
[deno-url]: https://github.com/stdlib-js/streams-node-debug/tree/deno
[deno-readme]: https://github.com/stdlib-js/streams-node-debug/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/streams-node-debug/tree/umd
[umd-readme]: https://github.com/stdlib-js/streams-node-debug/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/streams-node-debug/tree/esm
[esm-readme]: https://github.com/stdlib-js/streams-node-debug/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/streams-node-debug/blob/main/branches.md
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/streams-node-debug/main/LICENSE
[stream]: https://nodejs.org/api/stream.html
[object-mode]: https://nodejs.org/api/stream.html#stream_object_mode
[transform-stream]: https://nodejs.org/api/stream.html
[node-debug]: https://www.npmjs.com/package/debug
[@stdlib/streams/node/debug-sink]: https://github.com/stdlib-js/streams-node-debug-sink
[@stdlib/streams/node/inspect]: https://github.com/stdlib-js/streams-node-inspect