IoTReX: Functional Reactive Programming & Hardware

Sam Julien

Energy Trust of Oregon Dev, Treehouse Mentor, Maker

What We'll Cover

  • Quick Review of Hardware Side
  • Functional Reactive Programming & RxJS
  • Code & Demos
  • Where to Go From Here


Open Source Hardware + RxJS =

A Quick IoT Primer

  • A Second Industrial Revolution (hopefully without the robber-barons this time)
  • Connected devices!
  • Microcontrollers (dumb)
  • Raspberry Pi: Small, cheap computers (smart)

Learning Hardware & Electronics

Firmata & johnny-five

  • What's Firmata?
  • What's johnny-five?
  • How do I even?

What is FRP?

Functional Reactive Programming

  • Core concepts around for 20+ years
  • Why is this such a big thing (again)?
    • More data
    • More complexity
    • Greater demand to be asynchronous
  • Convergence of two big ideas:
    • Unidirectional (one-way) data flow
    • Return of Functional Programming

So new, it's 20 years old!

Let's Oversimplify All the Things

  • Functional programming
    • Pure functions with no side effects
    • Declarative over imperative
    • Example languages: Haskell, Scala, and recently Elm
    • In JavaScript, array functions like map, filter, and reduce are used in functional approaches
    • Not the be all, end all, just another skill like OOP

Reactive Programming

  • Reactive applications are asynchronous and event-driven
  • Think of an Excel spreadsheet
  • But what kinds of events?


  • A stream is a sequence of events over time
  • Anything can be a stream, from mouse clicks to data from a server
  • Streams can then be thought of as arrays of values and operated on as such. For example, mouse click coordinates: [(100,200), (300,400), (110,350)]

Put it Together: Functional Reactive Programming (FRP)

  • Entire applications can be built around streams
  • Create or identify the streams in your application, then combine and subscribe to them


  • Allows us to build in a declarative style by defining streams, how they are connected, and what happens as new values arrive over time
  • With little to no application state (state is typically stored on certain streams or the DOM)


  • RxJS is the JavaScript version of Microsoft's Reactive Extensions, which enable the creation of reactive applications with something called observables

What are Observables?

  • A data type introduced by RxJS to help us create, subscribe to, and react to streams
  • Asynchronous, push-based sequences of data that can be subscribed to
  • Think of them like an API for the stream, not the stream itself
Single return value
Multiple return values
Object Iterables (Array | Set | Map)
Push/Asynchronous/Reactive Promise Observable

Structure of an Observable

  • The Observable object contains onNext, onError, and onComplete methods that can invoke methods you specify
  • The observer subscribes to the event stream (the observable). The observable notifies the observer whenever an event occurs.
  • The subscribe method returns a Disposable object that allows you to clean up the subscription when you're done

Common RxJS Operators

var source$ = Rx.Observable.range(1,4); //1,2,3,4

//map (select) & flatMap (selectMany): changes each value 
//flatMap returns an observable so it works well with async operations
source$.map(x => x*2); //2, 4, 6, 8

//filter: returns only selected values based on custom logic
source$.filter(x => x % 2 === 0); //2, 4

//reduce: performs a computation on the stream and outputs the final value
source$.reduce((prev, curr) => prev + curr); //10

//scan: performs a computation on the stream but outputs intermittment values
source$.scan((prev, curr) => prev + curr); //1, 3, 6, 10

IoT + RxJS = IoTReX

  • Hardware circuit
  • Firmata
  • johnny-five
  • RxJS
  • (whatever else you want)


Code & Demos!

Improving on the Platform

What happens when you improve the...

  • ...device?
  • ...server?
  • ...front end?

Expanding Applications

What if we apply these concepts in...

  • ...industry?
  • ...agriculture?
  • justice?
  • ...cryptocurrency?

Where to Go From Here: IoT

Where to Go From Here: FRP

Go forth and stream!