Reactive programming with

Cycle.js

HELLO!

I am Luca MezzaliraSolutions Architect @ Massive Interactive

Google Developer Expert on Web Technologies

Community Manager of London JavaScript User Group

AGENDA

▸ Reactive programming

▸ Model - View - Intent

▸ Cycle.js

1.REACTIVE PROGRAMMING

PROGRAMMING PARADIGMSFUNCTIONALIt is a declarative programming paradigm, which means programming is done with expressions. In functional code, the output value of a function depends only on the arguments that are input to the function, so calling a function f twice with the same value for an argument x will produce the same result f(x) each time.

IMPERATIVEIt is a programming paradigm that uses statements that change a program's state. In much the same way that the imperative mood in natural languages expresses commands, an imperative program consists of commands for the computer to perform. Imperative programming focuses on describing how a program operates.

REACTIVEIt is a programming paradigm oriented around data flows and the propagation of change. This means that it should be possible to express static or dynamic data flows with ease in the programming languages used, and that the underlying execution model will automatically propagate changes through the data flow.

Imperative vs Reactive

REACTIVE PROGRAMMING IS PROGRAMMING WITH ASYNCHRONOUS DATA STREAMS

IS REACTIVE PROGRAMMING REALLY SO INTERESTING?

OBSERVER PATTERNThe observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods. It is mainly used to implement distributed event handling systems.

ITERATOR PATTERNIn object-oriented programming, the iterator pattern is a design pattern in which an iterator is used to traverse a container and access the container's elements. The iterator pattern decouples algorithms from containers

RxJS

“BACK-PRESSURE? WHAT?!Main obstacle when you approach for the first time Reactive Programming is the vocabulary.

My first suggestion is to familiarise with the domain, a lot of concepts become way easier if you understand what they mean before you start to work with them.

streams, hot observables, cold observables, marbles diagram, back-pressure, operators...

STREAMSA stream is a sequence of ongoing events ordered in time. It can emit three different things: a value (of some type), an error, or a "completed" signal.

EVERYTHING CAN BE A STREAM

COLD OBSERVABLESCold observables start running upon subscription: the observable sequence only starts pushing values to the observers when subscribe is called.

Values are also not shared among subscribers.

HOT OBSERVABLESWhen an observer subscribes to a hot observable sequence, it will get all values in the stream that are emitted after it subscribes.

The hot observable sequence is shared among all subscribers, and each subscriber is pushed the next value in the sequence.

OPERATORS▸ Creating Observables▸ Transforming Observables ▸ Filtering Observables▸ Combining Observables▸ Error Handling Operators▸ Mathematical Operators▸ Conditional Operators▸ Connectable Observables

Operators

reactivex.io/documentation/operators.html

MARBLES DIAGRAM

rxmarbles.com

2.MODEL VIEW INTENT

Architectures Timeline

90s

MVP

80s

MVC

2005

MVVM

2013

FLUX

2009

DCI

2015

MVI

VIEW INTENT

MODEL

RENDERER

futurice.com/blog/reactive-mvc-and-the-virtual-dom

MVI RULES▸ A module shouldn’t control

any other module (controller in MVC)

▸ The only shared part between modules are observables

▸ Intent is a component with only one responsibility: It should interpret what the user is trying to do in terms of model updates, and export these "user intentions" as events

VIEWInput: data events from the Model.

Output: a Virtual DOM rendering of the model, and raw user input events (such as clicks, keyboard typing, accelerometer events, etc).

VIEW

RENDERER

INTENTInput: raw user input events from the View.

Output: model-friendly user intention events.

INTENT

MODELInput: user interaction events from the Intent.

Output: data events.

MODEL

MVI PROs▸ Better separation of concern▸ Monodirectional flow▸ Dependency Injection▸ Applications become easier

to test (in particular views)▸ All the states live inside the

Model and the View is state-agnostic

3.Cycle.js

Cycle.jsCycle’s core abstraction is your application as a pure function main() where inputs are read effects (sources) from the external world and outputs (sinks) are write effects to affect the external world.

These side effects in the external world are managed by drivers: plugins that handle DOM effects, HTTP effects, etc.

CORE CONCEPTS▸ Objects▸ Functions▸ Drivers▸ Helpers

DRIVERSDrivers are functions that listen to Observable sinks (their input), perform imperative side effects, and may return Observable sources (their output).

http://cycle.js.org/drivers.html

Cycle.js DOMDriver

Cycle.js in action

thenewstack.io/developers-need-know-mvi-model-view-intent

Why not usingReactive Programming

in any project then?

THANKS EVERYONE

Q&A@lucamezzalira

www.lucamezzalira.com

www.londonjs.uk

mezzalab@gmail.com