# @promistream/debug

A stream for debugging pipelines. Logs everything that goes through it, via `console.debug`, and leaves it otherwise untouched.

Stream characteristics:
- __Promistream version:__ 0
- __Source stream:__ No
- __Transform stream:__ Yes
- __Sink stream:__ No
- __Buffering:__ None

Possible errors thrown:
- None (other than those being passed through from upstream).

## Example

This example is also included in the package in runnable form as `example.js`.

```js
"use strict";

const pipe = require("@promistream/pipe");
const fromIterable = require("@promistream/from-iterable");
const collect = require("@promistream/collect");
const debug = require("@promistream/debug");

(async function () {
	let result = await pipe([
		fromIterable([ 1, 2, 3, 4, 5 ]),
		debug("example pipeline"),
		collect()
	]).read();

	console.log(result);
})();
```

Example output (see the included screenshot.png for a colorized version):

```
[@promistream/debug][example pipeline] read was requested
[@promistream/debug][example pipeline] seen value: 1
[@promistream/debug][example pipeline] read was requested
[@promistream/debug][example pipeline] seen value: 2
[@promistream/debug][example pipeline] read was requested
[@promistream/debug][example pipeline] seen value: 3
[@promistream/debug][example pipeline] read was requested
[@promistream/debug][example pipeline] seen value: 4
[@promistream/debug][example pipeline] read was requested
[@promistream/debug][example pipeline] seen value: 5
[@promistream/debug][example pipeline] read was requested
[@promistream/debug][example pipeline] error thrown in read: EndOfStream: End of iterable reached
    at /home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/@promistream+from-iterable@0.1.0/node_modules/@promistream/from-iterable/index.js:26:10
    at /home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/@promistream+simple-source@0.1.4/node_modules/@promistream/simple-source/index.js:30:11
    at tryCatcher (/home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/bluebird@3.7.2/node_modules/bluebird/js/release/util.js:16:23)
    at Promise.attempt.Promise.try (/home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/bluebird@3.7.2/node_modules/bluebird/js/release/method.js:39:29)
    at getValue (/home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/@promistream+simple-source@0.1.4/node_modules/@promistream/simple-source/index.js:29:21)
    at /home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/@promistream+simple-source@0.1.4/node_modules/@promistream/simple-source/index.js:83:14
    at tryCatcher (/home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/bluebird@3.7.2/node_modules/bluebird/js/release/util.js:16:23)
    at Promise.attempt.Promise.try (/home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/bluebird@3.7.2/node_modules/bluebird/js/release/method.js:39:29)
    at Object.produceValue_simpleSource [as read] (/home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/@promistream+simple-source@0.1.4/node_modules/@promistream/simple-source/index.js:61:22)
    at produceValue_debug (/home/sven/projects/promistreams/streams/debug/index.js:27:30)
    at /home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/@promistream+simple-sink@0.1.1/node_modules/@promistream/simple-sink/index.js:45:20
    at tryCatcher (/home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/bluebird@3.7.2/node_modules/bluebird/js/release/util.js:16:23)
    at Promise.attempt.Promise.try (/home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/bluebird@3.7.2/node_modules/bluebird/js/release/method.js:39:29)
    at attemptRead (/home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/@promistream+simple-sink@0.1.1/node_modules/@promistream/simple-sink/index.js:44:23)
    at /home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/@promistream+simple-sink@0.1.1/node_modules/@promistream/simple-sink/index.js:52:13
    at tryCatcher (/home/sven/projects/promistreams/streams/debug/node_modules/.pnpm/bluebird@3.7.2/node_modules/bluebird/js/release/util.js:16:23) {
  _help: 'https://www.npmjs.com/package/error-chain',
  _promistreamIsEndOfStreamMarker: true,
  _promistreamVersion: 1
}
[ 1, 2, 3, 4, 5 ]
```

## API

### debug(label)

Creates a new debug stream.

- __label:__ *Optional.* The label to prefix the debug output with. Useful for distinguishing different pipelines, when multiple of them have a debug stream inserted at the same time.

__Returns:__ the new debug stream.