See Blog Post: Promises + FP = Beautiful Streams

Streams built using the following ingredients

• Promises
• Algebraic Data Types (ADT)

Hence the name ADT Streams.

• Usage
• Examples
• API
• Transpiling ES6 sources
• ES6 Promise polyfill

#Usage

##Server

In the server, install from npm

npm install adtstream

Then import

var Stream = require("adtstream").Stream;

Using the ES6 module syntax

import { Stream } from "adtstream";

In Node, you can create a stream from redeable Node stream

Stream.fromReadable( fs.createReadStream('test.txt') ).log('file')

You can also create a Stream from a Node EventEmitter

var server = http.createServer();
Stream.fromEmitter(server, 'request')

Using the generic Stream.bind() method you can implement your own stream

Stream.bind(subscribe, unsubscribe, untilP)

The function subscribes to an event source using the 1st argument, and yields results from the event source until the ending promise (the 3rd argument) completes then unsubscribes using the 2nd argument

For example here is how Streams are built from DOM events

Stream.fromDomEvent = function (target, event, untilP) {
  return Stream.bind(
    listener => target.addEventListener(event, listener),
    listener => target.removeEventListener(event, listener),
    untilP
  );
};

##Browser

In the browser the bundle exposes a global adts variable, so you can use it like

var Stream = adts.Stream;

Then you can create streams from dom events with the helper method $on

adts.$on(document, 'keydown').filter( e => e.keyCode === 17 ).log('key')

You can also use selectors in place of DOM objects

adts.$on('#button', 'click').log('click')

There is another utility method $once to get a Promise holding the next event occurrence

adts.$once(document, 'click').then( e => console.log(e) )

For example you can combine $on and $once to create finite event streams

adts.$on( document, 'mousemove', adts.$once('#stopButton', 'click') )

You can also use the timeout utility method delay to limit the event stream by a given delay (in milliseconds)

adts.$on( document, 'click', adts.utils.delay(1, 10000) ).log()

A common use case is to use the values from a stream to update some DOM element

adts.$on('#addButton', 'click')
    .scan( (p,c) => p + 1 )
    .forEach( v => document.querySelector('#output').textContent = v );

The library provides a helper method adts.$$ to express DOM updates declaratively (an alias for adts.utils.$update)

adts.$$('#output', {
  textContent : adts.$on('#addButton', 'click').scan( (p,c) => p + 1 )
})

There exists also a few additional goodies: virtual properties allow to encapsulate more elaborated updates.

adts.$$('#elem', { 
  css: { 
    class1 : aStream // toggle class1 based on aStream incoming value  
  }
});   // alias for target.disabled = !value
adts.$$('#elem', { enabled: aStream });   // target.disabled = !!value
adts.$$('#elem', { enabled: aStream });   // target.disabled = !value
adts.$$('#elem', { text : aStream });     // alias for textContent
adts.$$('#elem', { html : aStream });     // alias for innerHTML
adts.$$('#elem', { text : aStream });     // alias for textContent
adts.$$('#elem', { visible : aStream });  // alias for elem.style.display = 'none'/el.style.removeProperty('display')

You can add your own virtual properties using adts.$prop(prop, handler)

adts.$prop('greeting', (elem, value) => elem.innerHTML = 'Hi ' + value )

#Examples

1- classic up down

We've 2 buttons: up and down and an output text on the page, each click on up adds 1 to the output result while each click on down substracts 1 from the result

HTML

<button id="up">Up</button>
<button id="down">Down</button>
<p id="output"></p>

JavaScript

document.addEventListener("DOMContentLoaded", function(event) {
  var ups = adts.$on("#up", "click").map( _ => 1 ),
      downs = adts.$on("#down", "click").map( _ => -1 ),
    
  adts.$$('#output', { 
    text: ups.merge(downs).scan( (p,c) => p+c ) 
  })
});

2- Watchdog

This is an example taken from the SIGNAL programming language (a dataflow langauge), Here is the description (taken from The SIGNAL paper

A process emits an ORDER, to be executed within some DELAY. When finished, a DONE signal is made available. The WATCHDOG is designed to control this delay. It receives a copy of ORDER and DONE signals. It must emit an ALARM whenever a job is not finished in time

So we've 2 user commands : ORDER which initiates a new process, and DOWN which cancels an angoing process. W'll suppose that once an ORDER is emitted, the user is not allowed to emit any other ORDER until he explicitly clicks on DOWN

HTML

<p>
  <button id="order">Order</button> 
  <button id="done">Done</button>
</p>
<p>Timer <span id='timer' ></span></p>
<p>Counter <span id='counter' ></span></p>
<p id="alarm">Alarm <span  id="alarmText"></span></p>

JavaScript

var Stream = adts.Stream;

function watchdog( delay, tick, order, done ) {
	var counter = 
	  order.const(0).merge( done.const(-1) ).merge( tick.const(1) )
  		.scan( (prev,cur) => {
  			return 	cur <= 0  ? cur : // c == -1 => pause process, c == 0 => starts new order
  							prev < 0 ? prev :   // a tick event ? if process paused (p < 0) ignore it
  							prev + cur;        // else add to counter
  		}, -1)

	
	return {
	  counter : counter,
	  alarm   : counter.map( c => c > delay ).changes(), // boolean state (delay depassed), skip duplaicates
	  paused  : counter.map( c => c == -1 ).changes()    // boolean state
	};
}

document.addEventListener("DOMContentLoaded", function(event) {
	
  var tick = Stream.seconds(1000),
      order = adts.$on('#order', 'click'),
      done = adts.$on('#done', 'click'),
      wd = watchdog( 5, tick, order, done ); // a process has to be terminated in 5 seconds

  adts.$$('#done', { disabled: wd.paused });
  adts.$$('#order', { enabled: wd.paused });
  adts.$$('#counter', { text: wd.counter });

  adts.$$('#timer', { 
    text: tick.scan( (p,c) => p+1, 0) 
  });
  
  adts.$$('#alarmText', {
    text: wd.alarm.combine(wd.counter , (alarm, counter) => alarm ? counter : 'NA'; })
  });
	
  adts.$$('#alarm', { 
    css: { blink: wd.alarm }  
  });
	
});

#Transpiling ES6 sources

npm install to install dependencies; this will install dev dependencies Babel for ES6 transpilation and mocha for unit tests

Run the following commands :

• npm run compile to compile for Node.js, the compiled code will go to the lib directory
• npm run bundle to compile for the browser, compiled code go to the bundledirectory

Or simply use npm run build to execute both commands.

In the server, you can run the ES6 examples in the examples directory directly by

babel-node examples/[file.js]

This will compile the code in the fly and execute it.

#ES6 Promise polyfill

##Server environments

The server build uses the es6-promise polyfill to provide support for Promises (because actual stable versions of Node don't support Promise yet).

If you are using a server with native Promise support (iojs or latest Node version with --harmony flag) you can remove the first 2 lines from src/utils.js.

##Browser environments

In the browser build the polyfill is deactivated by default (see the browser field in package.json).

If you are using Chrome and Firefox you don't need to polyfill. Otherwise, you can check Promise support for your browser in this site

If you need to provide your own Promise support in the browser you can either

• remove the "es6-promise": false from package.json/browser field, or
• use a compliant Promise/A+ library, or