Reactive Programming with JavaScript

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Agenda• An Overview of JavaScript past and future

• Reactive Programming in a Nutshell

• What is Functional Programming

• Asynchronous JavaScript Applications

• Redux, Angular 2 and Reactive Programming

JavaScript

Why people hate it

• Lack of code organization, spaghetti code everywhere and abuse of globals

• Weird inheritance chain (aka prototype property)

• Callbacks are not straight forward to digest

• The mutability of the this keyword

Why people love it

• It has a rather low entry barrier; people can start coding and get results quickly

• It’s full of (legacy) examples to start with

• JavaScript is suited for the rest of us, continuously learning web hackers not having a PhD in CS

It’s your choice

JS, the New Assembly

• Everybody loves it but nobody wants really write it

• Some of the internals are hidden by popular frameworks (and people is happy about it)

• Only recently syntax and features get a relevant improvement (ES2015)

JS, What’s Next

Long Story Short• ECMAScript (ES) standardization started in 1996

• ES 3 was published in 1999 (the age of browsers war)

• ES 5 was published in 2009 (adoption started late 2011)

• ES6 was published in 2015 (early adoption)

• ES Next https://babeljs.io/docs/plugins/

What’s Changing

• The way of thinking in JavaScript (modules, scopes, arrow functions, classes, etc.)

• The support for asynchronous programming (async and await, promises, yield, etc.) tasks

• Math, Number, String, Array and object APIs re-evolution

Array & Arrow Functions

Array.from(document.querySelectorAll('*')) // Returns a real Array Array.of(1, 2, 3) // Similar to new Array(…),

[0, 0, 0].fill(7, 1) // [0,7,7] [1, 2, 3].find(x => x == 3) // 3 [1, 2, 3].findIndex(x => x == 2) // 1

[1, 2, 3, 4, 5].copyWithin(3, 0) // [1, 2, 3, 1, 2] ["a", "b", "c"].entries() // iterator [0, "a"], [1,"b"], [2,"c"] ["a", "b", "c"].keys() // iterator 0, 1, 2 ["a", "b", "c"].values() // iterator "a", "b", "c"

Classes & Inheritance// Pseudo-code of Array class Array { constructor(...args) { /* ... */ } static [Symbol.create]() { // Install special [[DefineOwnProperty]] // to magically update 'length' } }

// User code of Array subclass class MyArray extends Array { constructor(...args) { super(...args); } }

Proxy Objects

var target = {}; var handler = { get: function (receiver, name) { return `Hello, ${name}!`; } };

var p = new Proxy(target, handler); p.world === 'Hello, world!';

custom behavior for fundamental operations

Huge Impact

• Many new features and emerging standards

• Early browsers adoptions through transpilers (babeljs, traceur, etc.)

• Frameworks are adopting it (e.g. Angular 2, EmberJS, ReactJS, etc.)

Now Everything is Possible

Reactive Programming

In a Nutshell• Is a programming paradigm oriented around data

• Variables and property values get updated at runtime and the system is notified about changes

• Is similar to the well known observer pattern

• Supports different programming paradigms like Imperative, Object Oriented and Functional

Why It Matters• Enables developers creating data streams of

anything, not just from click and hover events

• Data streams emit events that can be handled asynchronously

• Data streams are data structures and then can be filtered

• Extends the asynchronous event engine of JavaScript to data flows

Reactive Systems

Reactive Systems• Responsive: the system responds in a timely manner

to data stream changes

• Elastic: the system stays responsive under varying workload

• Message Driven: the system relies on asynchronous not blocking message-passing

• Resilient: the system stays responsive in the face of failure (error handling)

Functional Programming

FP definition relies on foreboding statements like “functions as first-class objects” and “eliminating side

effects”

Definition

• All of your functions must accept at least one argument

• All of your functions must return data or another function

• No loops! (What???)

Getting Started

In Practicefunction totalForArray(currentTotal, arr) { currentTotal += arr[0];

// I am not using Array.shift on because // we're treating arrays as immutable. var remainingList = arr.slice(1);

// This function calls itself with the remainder of the list, and the // current value of the currentTotal variable if(remainingList.length > 0) { return totalForArray(currentTotal, remainingList); } // Unless the list is empty, in which case we return // the currentTotal value else { return currentTotal; } }

• First Class Functions: functions treated as objects, can be passed as arguments and returned as values

• Pure Functions: a function that doesn’t depend on and doesn’t modify the states of variables out of its scope

• Immutable Variables: a variable that preserves its original value after a mutation

Things I Like

First Class Functions

function analyticsHandler(e) { ...//perform some analytics. }

$('form').on('submit',analyticsHandler);

You really used jQuery? Yes, I am sorry! :)

Pure Functionsvar values = { a: 1 };

function impureFunction ( items ) { var b = 1;

items.a = items.a * b + 2; return items.a; } var c = impureFunction( values ); // Now `values.a` is 3

function pureFunction ( a ) { var b = 1;

a = a * b + 2;

return a; } var d = pureFunction( values.a ); // Values.a is not modified

Immutable Variables

var arr = new ImmutableArray([1, 2, 3, 4]); var v2 = arr.push(5);

arr.toArray(); // [1, 2, 3, 4] v2.toArray(); // [1, 2, 3, 4, 5]

• The data should be immutable (creating new data structures instead of modifying the ones that already exist)

• The app and its components should be stateless (no memory of previous execution)

App Perspective

It’s Not a Buzzword

• This book gives a lucid and thorough account of the concepts and techniques used in modern functional programming languages. Standard ML is used for notation, but the examples can be easily adapted to other functional languages.

• Originally published: January 1, 1989

• Author: Chris Reade

It’s a Science

Functional Reactive Programming

• Is a programming paradigm for reactive programming to which are applied the building blocks of functional programming (e.g. map, reduce, filter, merge, etc.)

• It’s implemented in JavaScript by popular libraries such as bacon.js and RxJS (sounds familiar Java developers?)

Bacon.js

var up = $('#up').asEventStream('click'); var down = $('#down').asEventStream('click');

var counter = // map up to 1, down to -1 up.map(1).merge(down.map(-1)) // accumulate sum .scan(0, function(x,y) { return x + y });

// assign the observable value to jQuery property text counter.assign($('#counter'), 'text');

Asynchronous

The Callback Hellvar p_client = new Db('integration_tests_20', new Server("127.0.0.1", 27017, {}), {'pk':CustomPKFactory}); p_client.open(function(err, p_client) { p_client.dropDatabase(function(err, done) { p_client.createCollection('test_custom_key', function(err, collection) { collection.insert({'a':1}, function(err, docs) { collection.find({'_id':new ObjectID("aaaaaaaaaaaa")}, function(err, cursor) { cursor.toArray(function(err, items) { test.assertEquals(1, items.length);

// Let's close the db p_client.close(); }); }); }); }); }); });

ES6 Promisesvar promise = new Promise(function(resolve, reject) { // do a thing, possibly async, then…

if (/* everything turned out fine */) { resolve("Stuff worked!"); } else { reject(Error("It broke")); } });

promise.then(function(result) { console.log(result); // "Stuff worked!" }, function(err) { console.log(err); // Error: "It broke" });

Async and Awaitvar request = require('request'); function getQuote() { var quote; return new Promise(function(resolve, reject) { request('http://ron-swanson-quotes.com/v2/quotes', function(error, response, body) { quote = body; resolve(quote); }); }); } async function main() { var quote = await getQuote(); console.log(quote); } main(); console.log('Ron once said,');

Asynchronous(made cool!)

Redux in a Nutshell• Redux is a predictable state container for JavaScript

applications

• Instead of mutating the state directly, you specify the mutations you want to happen with plain objects called actions

• Then you write a special function called a reducer to decide how every action transforms the entire application’s state

• You should always return the state of the app

Redux Actions“Actions are payloads of information that send data

from your application to your store”

{ type: 'ADD_TODO', text: 'Use Redux' } { type: 'REMOVE_TODO', id: 42 } { type: 'LOAD_ARTICLE', response: { ... } }

Redux Reducers

“Actions describe the fact that something happened, then a reducer handle the event and eventually

update the app state”

Redux Reducersimport * as TodoActions from './todoActions';

const initialState = { todos: [], currentFilter: 'SHOW_ALL' }

export function rootReducer(state = initialState, action){ switch (action.type) { case TodoActions.ADD_TODO: return { todos: state.todos.concat({ id: action.id, text: action.text, completed: action.completed }), currentFilter: state.currentFilter }; case TodoActions.TOGGLE_TODO: return {}; // Continue... } }

Redux Stores“A Redux store is the object that brings together actions

and reducers offering a centralized way to dispatch actions and access the app state”

import { createStore } from 'redux' import todoApp from './reducers' import { addTodo} from './actions'

let store = createStore(todoApp)

// Log the initial state console.log(store.getState())

// Dispatch some actions store.dispatch(addTodo('Learn about actions'))

Redux Data Flow• You call store.dispatch(action)

• The store calls the reducer function you gave it

• The root reducer may combine the output of multiple reducers into a single state tree

• The store saves the complete state tree returned by the root reducer

How it Sounds?

Angular 2

Tech Stack• TypeScript

• RxJS

• JSPM or WebPack

• Grunt (seriously?!?) or Gulp

• Karma + Jasmine or (Mocha + Chai)

TypeScript

• A super set of JavaScript developed by Microsoft

• Implements classes, interfaces, inheritance, strict data typing, private properties and methods, etc.

• Angular Team choice for the next version of Angular (Microsoft and Google are now buddies!)

• A reactive streams library that allows you to work with asynchronous data streams

• Combines Observables and Operators so we can subscribe to streams and react to changes using composable operations

RxJS, hello world!

$scope.counter = 0; rx.Observable .interval(1000) .take(3) .safeApply($scope, function(x) { $scope.counter = x; }) .subscribe(); // shows 0, 1, 2

Integrating Redux$ npm install angular2-redux

import {AppStore} from "angular2-redux"; import {bootstrap} from "angular2/platform/browser"; // create factory to be called once angular has been bootstrapped const appStoreFactory = () => { let reduxAppStore; // create redux store // ... return new AppStore(reduxStore); }; // bootstrap angular bootstrap(MyAppComponent,[provide(AppStore, { useFactory: appStoreFactory })]);

Demohttps://plnkr.co/edit/3mhKoOOAKJp27E2FpIOq

Wait a second…

Reactive Programming, functional programming and OOP?

Using Functions Properly• Keep your functions pure

• Use your functions as arguments

• Write small reusable functions

• Return functions if needed

• Always return a value

Taking Advantages from RxJSimport {Http} from 'angular2/http'; import {Observable} from 'rxjs/Observable'; import {Observer} from 'rxjs/Observer'; import 'rxjs/add/operator/share'; import {Todo} from 'app/interfaces';

export class TodosService { todos$: Observable<Todo[]>; private _todosObserver: Observer<Todo[]>; private _dataStore: { todos: Todo[] }; constructor(private _http: Http) { // Create Observable Stream to output our data this.todos$ = new Observable(observer => this._todosObserver = observer).share(); this._dataStore = { todos: [] }; } }

Embracing Redux Data Flows

• Decouple your dependencies by implementing event driven architecture

• Keep the app state predictable by returning a new state

Questions and Answers

–Giorgio Natili

“Keep calm and rock ‘n roll the Codemotion!”

Thanks!

Reactive Programming with JavaScript

Internet

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