My presentation on KyivJS 30-01-2016

1. Scala-JS

2. 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

3. coffeescript, typescript, clojurescript etc.
List of languages that compile to JS

4. OMG
more than 300

5. Curious javascript problems
javascript> ["10", "10", "10", "10"].map(parseInt)
[10, NaN, 2, 3]
wtfjs.com

6. 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

7. Martin Odersky
invented Scala
co-author Java generics
he wrote a compiler for Java
he wrote a compiler for Scala
www.coursera.org/course/progfun

8. Companies which choose scala

9. Elitism Scala
Scala 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

10. Java code
public 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;
}
}

11. Scala code
class Person(val firstName: String, val lastName: String)

12. 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)

13. Scala.js developers
1207 commits 702 commits

14. Code examples: classes
class Person {
constructor(firstName, lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
fullName() {
return `${this.firstName} ${this.lastName}`;
}
}
ES6
class Person(val firstName: String, val
lastName: String) {
def fullName(): String =
s"$firstName $lastName"
}
Scala.js

15. 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} = ${person.firstName}`);
}
}
ES6
val personMap = Map(
10 -> new Person("Roger", "Moore"),
20 -> new Person("James", "Bond")
)
val names = for {
(key, person) <- personMap
if key > 15
} yield s"$key = ${person.firstName}"
Scala.js

16. Compiler output code
object Main extends js.JSApp{
def main() = {
var x = 0
while(x < 10) x += 3
println(x)
// 12
}
}
Scala.js
ScalaJS.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

17. 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/

18. HelloApp
package helloapp.webapp
import scala.scalajs.js.JSApp
object HelloApp extends JSApp {
def main(): Unit = {
println("Hello world!")
}
}

19. Using the DOM
Adding 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)
}

20. Reacting on User Input
import 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>

21. Using jQuery
Adding the DOM library to build.sbt
import org.scalajs.jquery.jQuery
jQuery("body").append("<p>[message]</p>")

22. Testing
package 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

23. 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

24. expansion of consciousness

25. 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

26. Benchmarks

27. Where to use it?
SPA
Enterprise application
Games много кода

29. ?