Scala js (kyiv js 30-01)

Scala-JS

About me

Evgeniy Safronov

I am from Kherson

Software engineer in RIFL Media LLC

I love to write in JS and talk about JS

contacts:

evgeniy.safronov@outlook.com

skype: lambda.omega1

github.com/javacodegeek

coffeescript, typescript, clojurescript etc.

List of languages that compile to JS

OMG

more than 300

https://github.com/jashkenas/coffeescript/wiki/List-of-languages-that-compile-to-JS

Curious javascript problems

javascript> ["10", "10", "10", "10"].map(parseInt)

[10, NaN, 2, 3]

wtfjs.com

Scala profile● started in 2001 at the École Polytechnique Fédérale de Lausanne by Martin

Odersky

● functional programming and object oriented programming

● very strong static type system

● was released in 2004 on JVM and .NET

● v2.0 followed in March 2006

www.scala-lang.org

Martin Oderskyinvented Scala

co-author Java generics

he wrote a compiler for Java

he wrote a compiler for Scala

www.coursera.org/course/progfun

Companies which choose scala

Elitism ScalaScala developers are expensive

High barrier to entry

The successful combination of functional and object-oriented paradigms

Wide range of applications

Functional programming with immutable variables, lambdas, closures, lists, and so on

Java codepublic class Person {

private final String firstName;

private final String lastName;

public Person(String firstName, String lastName) {

this.firstName = firstName;

this.lastName = lastName;

}

public String getFirstName() {

return firstName;

}

public String getLastName() {

return lastName;

}

}

Scala code

class Person(val firstName: String, val lastName: String)

Back to curious javascript problems

javascript> ["10", "10", "10", "10"].map(parseInt)

[10, NaN, 2, 3]

scala> List("10", "10", "10", "10").map(parseInt)

List(10, 10, 10, 10)

Scala.js developers

1207 commits 702 commits

Code examples: classes

class Person {

constructor(firstName, lastName) {

this.firstName = firstName;

this.lastName = lastName;

}

fullName() {

return `${this.firstName} ${this.lastName}`;

}

}

ES6class Person(val firstName: String, val

lastName: String) {

def fullName(): String =

s"$firstName $lastName"

}

Scala.js

Code examples: collections

const personMap = new Map([

[10, new Person("Roger", "Moore")],

[20, new Person("James", "Bond")]

]);

const names = [];

for (const [key, person] of personMap) {

if (key > 15) {

names.push(`${key} = ${person.firstName}`);

}

}

ES6val personMap = Map(

10 -> new Person("Roger", "Moore"),

20 -> new Person("James", "Bond")

)

val names = for {

(key, person) <- personMap

if key > 15

} yield s"$key = ${person.firstName}"

Scala.js

Compiler output code

object Main extends js.JSApp{

def main() = {

var x = 0

while(x < 10) x += 3

println(x)

// 12

}

}

Scala.jsScalaJS.c.LMain$.prototype.main__V =

(function() {

var x = 0;

while ((x < 10)) {

x = ((x + 3) | 0)

};

ScalaJS.m.s_Predef$()

.println__O__V(x)

// 12

});

ES5

How to install?install sbt (scala build tool)

config plugin ”sbt-scalajs”

Rhino presents out of the box, but you can setup V8.

http://www.scala-js.org/tutorial/basic/

HelloApppackage helloapp.webapp

import scala.scalajs.js.JSApp

object HelloApp extends JSApp {

def main(): Unit = {

println("Hello world!")

}

}

Using the DOMAdding the DOM library to build.sbt

import org.scalajs.dom

import dom.document

def appendPar(targetNode: dom.Node, text: String): Unit = {

val parNode = document.createElement("p")

val textNode = document.createTextNode(text)

parNode.appendChild(textNode)

targetNode.appendChild(parNode)

}

Reacting on User Inputimport scala.scalajs.js.annotation.JSExport

@JSExport

def addClickedMessage(): Unit = {

appendPar(document.body, "You clicked the button!")

}

<button id=”click-me-button” type=”button” onClick=”tutorial.webapp.MyApp().

addClickedMessage()”>Click me!</button>

Using jQuery

Adding the DOM library to build.sbt

import org.scalajs.jquery.jQuery

jQuery("body").append("<p>[message]</p>")

Testingpackage tutorial.webapp

import utest._

import org.scalajs.jquery.jQuery

object MyTest extends TestSuite {

// Initialize App

HelloApp.setupUI()

def tests = TestSuite {

HelloWorld {

assert(jQuery("p:contains('Hello World')").length == 1)

}

}

}

github.com/lihaoyi/utest

Why you should try Scala.js

New paradigms

All power of Scala

Very good IDE support (IntelliJ Scala and Eclipse ScalaDE)

Scala community

Universal application

expansion of consciousness

Scala.js the official Scala to JavaScript compiler http://www.scala-js.org/

https://github.com/scala-js/scala-js

https://gitter.im/scala-js/scala-js

Github info:

● 3121 commits● 41 contributors ● issues 82/1064 open/close● 36 releases● 2098 stars ● 188 forks

Benchmarks

Where to use it?SPA

Enterprise application

Games много кода

?