🧣 🏪 ✒️ Prática em Kotlin: Criação de aplicativos da web em React e Kotlin / JS 🌿 ◀️ 🚣🏼

De um tradutor .

Ei! Existe um estereótipo sobre o Kotlin de que é uma linguagem para desenvolvimento apenas para Android. Na verdade, não é bem assim: a linguagem suporta oficialmente várias plataformas ( JVM , JS , Native ), e também sabe trabalhar com bibliotecas para essas plataformas escritas em outras linguagens. Esse suporte para "multiplataforma" permite não apenas escrever todos os tipos de projetos em uma linguagem em uma única forma, mas também reutilizar o código ao escrever um projeto para diferentes plataformas.

Neste artigo, estou traduzindo o tutorial prático oficial do Kotlin sobre a criação de sites em Kotlin. Cobriremos muitos aspectos da programação Kotlin / JS e entenderemos como trabalhar com mais do que apenas um DOM puro. Falaremos principalmente sobre React JS , mas também falaremos sobre o sistema de compilação do Gradle , usando dependências do NPM , chamando a API REST , implantando no Heroku e, por fim, criando um aplicativo reprodutor de vídeo .

O texto é dirigido a quem conhece um pouco Kotlin e não conhece ou mal conhece React. Se você tiver mais experiência nesses assuntos, algumas partes do tutorial podem parecer excessivamente mastigadas para você.

kotlin-react

, .

. , 09.04.2021.

1.

, Kotlin/JS React . React , . , .

React , - . JavaScript.

Kotlin/JS React, Gradle org.jetbrains.kotlin.js

. , React .

, - (DSL) , . , , .

, , HTML CSS. , .

KotlinConf , . KotlinConf 2018 - 1300 . YouTube, – "". – KotlinConf Explorer (. ).

Resultado

, , GitHub. , .

, .

2.

, , . , – IntelliJ IDEA ( 2020.3

, Community Edition) (1.4.30

) – . , ( Windows, MacOS Linux).

, .

GitHub IntelliJ IDEA (, File | New | Project from Version Control... Git | Clone...).

Kotlin/JS Gradle , - . Gradle , .

, , .

: , , Gradle , – .

Gradle

React, , . Gradle , .

, build.gradle.kts

repositories

. .

dependencies

:

dependencies {
    // React, React DOM + Wrappers ( 3)
    implementation("org.jetbrains:kotlin-react:17.0.1-pre.148-kotlin-1.4.21")
    implementation("org.jetbrains:kotlin-react-dom:17.0.1-pre.148-kotlin-1.4.21")
    implementation(npm("react", "17.0.1"))
    implementation(npm("react-dom", "17.0.1"))

    // Kotlin Styled ( 3)
    implementation("org.jetbrains:kotlin-styled:5.2.1-pre.148-kotlin-1.4.21")
    implementation(npm("styled-components", "~5.2.1"))

    // Video Player ( 7)
    implementation(npm("react-youtube-lite", "1.0.1"))

    // Share Buttons ( 7)
    implementation(npm("react-share", "~4.2.1"))

    // Coroutines ( 8)
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.4.3")
}

, IDEA Gradle . , Reimport All Gradle Projects - Gradle ( ).

HTML

JavaScript , JS HTML , . src/main/resources/index.html

:

<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Hello, Kotlin/JS!</title>
</head>
<body>
    <div id="root"></div>
    <script src="confexplorer.js"></script>
</body>
</html>

Kotlin/JS Gradle , ("") JavaScript , . HTML confexplorer.js

(, , , followingAlong

, followingAlong.js

).

JavaScript, ( #root

) . , , .

: HTML, , onLoad

body

. Kotlin/JS body

.

"Hello, World" , – , . , . src/main/kotlin/Main.kt

:

import kotlinx.browser.document

fun main() {
    document.bgColor = "red"
}

Kotlin/JS Gradle webpack-dev-server, IDE .

, run

browserDevelopmentRun

- Gradle. other

( ), kotlin browser

:

Tarefa de inicialização do servidor

IDE, , ./gradlew run

( Windows Gradle -: .\gradlew.bat run

).

, , , :

Página vermelha

(hot reload) a.k.a.

, – Kotlin/JS . run

Gradle.

, ( IDE – Stop; – Ctrl+C

).

IDEA, . IDEA , Gradle , :

Edição de abertura

Run/Debug Configurations --continuous

:

Adicionando um argumento

Run (|>

) .

, : ./gradlew run --continuous

.

, Gradle . , :

document.bgColor = "blue"

, , – .

. . , .

, , , . -, , - . -, , . -, - , , Gradle , – - .

, Kotlin/JS, . , : HTML . browserDevelopmentWebpack

, build/distributions

build/developmentExecutable

. index.html

, .

, ...

Kotlin/JS , . !

master

.

3. –

Hello, World. .

src/main/kotlin/Main.kt

:

import react.dom.*
import kotlinx.browser.document

fun main() {
    render(document.getElementById("root")) {
        h1 {
            +"Hello, React+Kotlin/JS!"
        }
    }
}

:

Olá Mundo

, ! , . render

kotlin-react-dom ( ) . , src/main/resources/index.html

ID root

, . – . , HTML , DSL.

HTML

kotlin-react DSL, HTML . , DSL .

, . , - , , !

+

:

– +

. . h1

– , . +

, unaryPlus

, HTML .

, +

" ".

HTML

, , () HTML. HTML, . , HTML:

<h1>KotlinConf Explorer</h1>
<div>
    <h3>Videos to watch</h3>
    <p>John Doe: Building and breaking things</p>
    <p>Jane Smith: The development process</p>
    <p>Matt Miller: The Web 7.0</p>

    <h3>Videos watched</h3>
    <p>Tom Jerry: Mouseless development</p>
</div>
<div>
    <h3>John Doe: Building and breaking things</h3>
    <img src="https://via.placeholder.com/640x360.png?text=Video+Player+Placeholder">
</div>

Kotlin DSL. . , , :

h1 {
    +"KotlinConf Explorer"
}
div {
    h3 {
        +"Videos to watch"
    }
    p {
        +"John Doe: Building and breaking things"
    }
    p {
        +"Jane Smith: The development process"
    }
    p {
        +"Matt Miller: The Web 7.0"
    }

    h3 {
        +"Videos watched"
    }
    p {
        +"Tom Jerry: Mouseless development"
    }
}
div {
    h3 {
        +"John Doe: Building and breaking things"
    }
    img {
       attrs {
           src = "https://via.placeholder.com/640x360.png?text=Video+Player+Placeholder"
       }
    }
}

render

. IntelliJ IDEA , (quick-fixes) Alt+Enter

. , :

kotlinconf-placeholder

HTML DSL HTML. – , . , , , – HTML DSL , .

- . KotlinVideo

, ( Main.kt

, – ), external

– , API:

external interface Video {
    val id: Int
    val title: String
    val speaker: String
    val videoUrl: String
}

data class KotlinVideo(
    override val id: Int,
    override val title: String,
    override val speaker: String,
    override val videoUrl: String
) : Video

: . Main.kt

:

val unwatchedVideos = listOf(
    KotlinVideo(1, "Building and breaking things", "John Doe", "https://youtu.be/PsaFVLr8t4E"),
    KotlinVideo(2, "The development process", "Jane Smith", "https://youtu.be/PsaFVLr8t4E"),
    KotlinVideo(3, "The Web 7.0", "Matt Miller", "https://youtu.be/PsaFVLr8t4E")
)

val watchedVideos = listOf(
    KotlinVideo(4, "Mouseless development", "Tom Jerry", "https://youtu.be/PsaFVLr8t4E")
)

HTML, , ! HTML . p

, :

for (video in unwatchedVideos) {
    p {
        +"${video.speaker}: ${video.title}"
    }
}

watchedVideos

. , . , , , , .

CSS

, , : , . - .css

index.html

, , Kotlin DSL – CSS.

kotlin-styled styled-components , . CSS-in-JS. , , .

CSS DSL, Gradle. :

dependencies {
    //...
    // Kotlin Styled ( 3)
    implementation("org.jetbrains:kotlin-styled:5.2.1-pre.148-kotlin-1.4.21")
    implementation(npm("styled-components", "~5.2.1"))
    //...
}

div

h3

styled

, , styledDiv

styledH3

. css

. , , :

styledDiv {
    css {
        position = Position.absolute
        top = 10.px
        right = 10.px
    }
    h3 {
        +"John Doe: Building and breaking things"
    }
    img {
        attrs {
            src = "https://via.placeholder.com/640x360.png?text=Video+Player+Placeholder"
        }
    }
}

, IDEA . , :

import kotlinx.css.*
import styled.*

Alt+Enter

.

. – , . CSS Grids, ( ). ( fontFamily

) ( sans-serif

), , , ( color

).

step-02-first-static-page

.

4. React – .

. , , . , , / .

, . , :

componente raiz

, , :

componentes de divisão

. App

, . App.kt

src/main/kotlin

. App

, RComponent

( React Component). (RProps

RState

), :

import react.*

@JsExport
class App : RComponent<RProps, RState>() {

    override fun RBuilder.render() {
        //    HTML!
    }
}

HTML render

. . main

- App

. : App

, child

:

fun main() {
    render(document.getElementById("root")) {
        child(App::class) {}
    }
}

, . , .

? , – . , , .

VideoList.kt

. App

, VideoList

, RComponent

HTML DSL unwatchedVideos

:

import react.*
import react.dom.*

@JsExport
class VideoList : RComponent<RProps, RState>() {

    override fun RBuilder.render() {
        for (video in unwatchedVideos) {
            p {
                +"${video.speaker}: ${video.title}"
            }
        }
    }
}

App

:

div {
    h3 {
        +"Videos to watch"
    }
    child(VideoList::class) {}

    h3 {
        +"Videos watched"
    }
    child(VideoList::class) {}
}

: App

. . , .

, - . , , . props

. , .

, . . VideoList.kt

:

external interface VideoListProps : RProps {
    var videos: List<Video>
}

VideoList

, :

@JsExport
class VideoList : RComponent<VideoListProps, RState>() {

    override fun RBuilder.render() {
        for (video in props.videos) {
            p {
                key = video.id.toString()
                +"${video.speaker}: ${video.title}"
            }
        }
    }
}

( , ), key

. , , – ! , , .

, VideoList

( App

) . unwatchedVideos

watchedVideos

:

child(VideoList::class) {
    attrs.videos = unwatchedVideos
}

, , . , . , .

, , . , : , , :

fun RBuilder.videoList(handler: VideoListProps.() -> Unit): ReactElement {
    return child(VideoList::class) {
        attrs.handler()
    }
}

, : videoList

RBuilder

. handler

– - VideoListProps

, Unit

. child

( VideoList

), handler

attrs

.

– :

videoList {
    videos = unwatchedVideos
}

, child

, class

attrs

, . , . ! App

.

- – . , . : alert

.

VideoList.render

. , p

:

p {
    key = video.id.toString()
    attrs {
        onClickFunction = {
            window.alert("Clicked $video!")
        }
    }
    +"${video.speaker}: ${video.title}"
}

IntelliJ IDEA , Alt+Enter

. :

import kotlinx.html.js.onClickFunction
import kotlinx.browser.window

:

alerta

onClickFunction

, . Kotlin/JS . . , onClickFunction

.

. (|>

). – . – :

external interface VideoListState : RState {
    var selectedVideo: Video?
}

VideoList

, VideoListState

– RComponent<..., VideoListState>

.
.
onClickFunction

selectedVideo

, . , setState

.

, :

@JsExport
class VideoList : RComponent<VideoListProps, VideoListState>() {

    override fun RBuilder.render() {
        for (video in props.videos) {
            p {
                key = video.id.toString()
                attrs {
                    onClickFunction = {
                        setState {
                            selectedVideo = video
                        }
                    }
                }
                if (video == state.selectedVideo) {
                    +"|> "
                }
                +"${video.speaker}: ${video.title}"
            }
        }
    }
}

setState

. UI .

, React FAQ.

step-03-first-component

.

5. .

. , , . , :)

par

-, – , . ( ) . ( , "" ).

-, : . , . , , . . ! , App

. , VideoList

.

external interface AppState : RState {
    var currentVideo: Video?
}

App

:

@JsExport
class App : RComponent<RProps, AppState>()

VideoListState

, . , , :

@JsExport
class VideoList : RComponent<VideoListProps, RState>()

App

VideoList

. VideoListProps

, :

external interface VideoListProps : RProps {
    var videos: List<Video>
    var selectedVideo: Video?
}

, :

if (video == props.selectedVideo) {
    +"|> "
}

, : , setState

onClickFunction

. , - .

, , . -: . , ? – , Video

Unit

:

external interface VideoListProps : RProps {
    var videos: List<Video>
    var selectedVideo: Video?
    var onSelectVideo: (Video) -> Unit
}

onClickFunction

:

onClickFunction = {
    props.onSelectVideo(video)
}

, . , . videoList

:

videoList {
    videos = unwatchedVideos
    selectedVideo = state.currentVideo
    onSelectVideo = { video ->
        setState {
            currentVideo = video
        }
    }
}

watchedVideos

.

, : , , . , , .

step-04-composing-components

.

6. !

, . .

, – ( -). , : , . , Video

, . VideoPlayer

VideoPlayer.kt

:

import kotlinx.css.*
import kotlinx.html.js.onClickFunction
import react.*
import react.dom.*
import styled.*

external interface VideoPlayerProps : RProps {
    var video: Video
}

@JsExport
class VideoPlayer : RComponent<VideoPlayerProps, RState>() {
    override fun RBuilder.render() {
        styledDiv {
            css {
                position = Position.absolute
                top = 10.px
                right = 10.px
            }
            h3 {
                +"${props.video.speaker}: ${props.video.title}"
            }
            img {
                attrs {
                    src = "https://via.placeholder.com/640x360.png?text=Video+Player+Placeholder"
                }
            }
        }
    }
}

fun RBuilder.videoPlayer(handler: VideoPlayerProps.() -> Unit): ReactElement {
    return child(VideoPlayer::class) {
        this.attrs(handler)
    }
}

styledDiv

( App.kt

) . , - – let

, let

, currentVideo

null

:

state.currentVideo?.let { currentVideo ->
    videoPlayer {
        video = currentVideo
    }
}

. VideoPlayer

.

, VideoPlayer

. , .

-. , , , , . .

VideoPlayerProps

:

external interface VideoPlayerProps : RProps {
    var video: Video
    var onWatchedButtonPressed: (Video) -> Unit
    var unwatchedVideo: Boolean
}

, . CSS : . HTML DSL render

, h3

img

:

styledButton {
    css {
        display = Display.block
        backgroundColor = if (props.unwatchedVideo) Color.lightGreen else Color.red
    }
    attrs {
        onClickFunction = {
            props.onWatchedButtonPressed(props.video)
        }
    }
    if (props.unwatchedVideo) {
        +"Mark as watched"
    } else {
        +"Mark as unwatched"
    }
}

VideoPlayer

, .

unwatched

watched

, .

. ! :

external interface AppState : RState {
    var currentVideo: Video?
    var unwatchedVideos: List<Video>
    var watchedVideos: List<Video>
}

init

. , App

:

override fun AppState.init() {
    unwatchedVideos = listOf(
        KotlinVideo(1, "Building and breaking things", "John Doe", "https://youtu.be/PsaFVLr8t4E"),
        KotlinVideo(2, "The development process", "Jane Smith", "https://youtu.be/PsaFVLr8t4E"),
        KotlinVideo(3, "The Web 7.0", "Matt Miller", "https://youtu.be/PsaFVLr8t4E")
    )
    watchedVideos = listOf(
        KotlinVideo(4, "Mouseless development", "Tom Jerry", "https://youtu.be/PsaFVLr8t4E")
    )
}

unwatchedVideos

watchedVideos

Main.kt

, Main.kt

(un

)watchedVideos

, IDE , state.

(un

)watchedVideos

.

, . :

videoPlayer {
    video = currentVideo
    unwatchedVideo = currentVideo in state.unwatchedVideos
    onWatchedButtonPressed = {
        if (video in state.unwatchedVideos) {
            setState {
                unwatchedVideos -= video
                watchedVideos += video
            }
        } else {
            setState {
                watchedVideos -= video
                unwatchedVideos += video
            }
        }
    }
}

, , , .

, . , , , . !

. .

step-05-more-components

.

7. NPM

, . , , . , , .

– .

, . react-youtube-lite

. API README.

. react-youtube-lite

, Gradle. :

dependencies {
    // ...
    // Video Player ( 7)
    implementation(npm("react-youtube-lite", "1.0.1"))
    // ...
}

– NPM Gradle npm

. yarn

, Kotlin/JS Gradle , , .

NPM , : , . , IDE . . ReactYouTube.kt

:

@file:JsModule("react-youtube-lite")
@file:JsNonModule

import react.*

@JsName("ReactYouTubeLite")
external val reactPlayer: RClass<dynamic>

JavaScript – , , . – require("react-youtube-lite").default

JS. : " , , RClass<dynamic>

".

, , . dynamic

, . , , - (, ).

, , ( external

), README . – . , – . :

@file:JsModule("react-youtube-lite")
@file:JsNonModule

import react.*

@JsName("ReactYouTubeLite")
external val reactPlayer: RClass<ReactYouTubeProps>

external interface ReactYouTubeProps : RProps {
    var url: String
}

VideoPlayer

! img

:

reactPlayer {
    attrs.url = props.video.videoUrl
}

KotlinConf ( ). – . , , . , , react-share. Gradle:

dependencies {
    // ...
    // Share Buttons ( 7)
    implementation(npm("react-share", "~4.2.1"))
    // ...
}

. , , : , EmailShareButton

EmailIcon

. . ; ReactShare.kt

:

@file:JsModule("react-share")
@file:JsNonModule

import react.RClass
import react.RProps

@JsName("EmailIcon")
external val emailIcon: RClass<IconProps>

@JsName("EmailShareButton")
external val emailShareButton: RClass<ShareButtonProps>

@JsName("TelegramIcon")
external val telegramIcon: RClass<IconProps>

@JsName("TelegramShareButton")
external val telegramShareButton: RClass<ShareButtonProps>

external interface ShareButtonProps : RProps {
    var url: String
}

external interface IconProps : RProps {
    var size: Int
    var round: Boolean
}

. reactPlayer

( styledDiv

, ):

styledDiv {
    css {
        display = Display.flex
        marginBottom = 10.px
    }
    emailShareButton {
        attrs.url = props.video.videoUrl
        emailIcon {
            attrs.size = 32
            attrs.round = true
        }
    }
    telegramShareButton {
        attrs.url = props.video.videoUrl
        telegramIcon {
            attrs.size = 32
            attrs.round = true
        }
    }
}

, . , . , , .

par

, .

step-06-packages-from-npm

.

8. REST API

, . , REST API.

API, https://my-json-server.typicode.com/kotlin-hands-on/kotlinconf-json/videos/1. API – videos

, . API . , , Video

( ;)

). , .

JS

. Kotlin/JS , . Fetch API, HTTP REST API.

JavaScript – . , , . , - . , , , . , :

window.fetch("https://url...").then {
    it.json().then {
        it.unsafeCast<Video>()
        //...
    }
}

. , .

(structured concurrency) – . , . . .

, Gradle :

dependencies {
    //...
    // Coroutines ( 8)
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.9")
}

, !

App.kt

, , REST API:

suspend fun fetchVideo(id: Int): Video {
    val response = window
        .fetch("https://my-json-server.typicode.com/kotlin-hands-on/kotlinconf-json/videos/$id")
        .await()
        .json()
        .await()
    return response as Video
}

. :

import kotlinx.browser.window
import kotlinx.coroutines.*

, suspend . fetch

, id

API. (await

), JSON, . external interface Video

. , IDE – JavaScript fetch

: , Video

. . : , @Suppress

, unsafeCast

(response.unsafeCast<Video>()

).

. window.fetch

json

. , . , (await

) . , , . await

, ( suspend

). , .

suspend

, , 25. fetchVideos

, 25 . , suspend – async

. :

suspend fun fetchVideos(): List<Video> = coroutineScope {
    (1..25).map { id ->
        async {
            fetchVideo(id)
        }
    }.awaitAll()
}

coroutineScope

. 25 , , .

, .

. , init

App

:

override fun AppState.init() {
    unwatchedVideos = listOf()
    watchedVideos = listOf()

    val mainScope = MainScope()
    mainScope.launch {
        val videos = fetchVideos()
        setState {
            unwatchedVideos = videos
        }
    }
}

, init

, setState

unwatchedVideos

. - , , , unwatchedVideos

. setState

, , .

:

dados reais

. , "Hello, World" .

, , , , .

step-07-using-external-rest-api

.

9.

, Gradle build

- IntelliJ IDEA ./gradlew build

. , , , DCE (dead code elimination – ).

, build/distributions

. JS , HTML , . , , , HTTP , GitHub Pages .

Heroku

Heroku . ; , .

git Heroku . :

git init
heroku create
git add .
git commit -m "initial commit"

JVM , Heroku (, Ktor Spring Boot), , . Heroku:

heroku buildpacks:set heroku/gradle
heroku buildpacks:add https://github.com/heroku/heroku-buildpack-static.git

heroku/gradle

stage

Gradle . , build

, , :

// Heroku Deployment ( 9)
tasks.register("stage") {
    dependsOn("build")
}

buildpack-static

, static.json

. root

:

{
    "root": "build/distributions"
}

, , :

git add -A
git commit -m "add stage task and static content root configuration"
git push heroku master

master (, , step*

), , master Heroku (, : git push heroku step-08-deploying-to-production:master

).

, , !

heroku

final

.

10. :

- , .

React 16.8 . . : !

, , – state effect. , .

, . , . – this

. , , :

external interface WelcomeProps : RProps {
    var name: String
}

val welcome = functionalComponent<WelcomeProps> { props -> 
    h1 {
        +"Hello, ${props.name}"
    }
}

, external interface

. . functionalComponent

render

.

: child

:

child(welcome) {
    attrs.name = "Kotlin"
}

fun RBuilder.welcome(handler: WelcomeProps.() -> Unit) = child(welcome) {
    attrs.handler()
}

4. welcome { name = "Kotlin" }

.

, - . .

State

, . :

val counter = functionalComponent<RProps> {
    val (count, setCount) = useState(0)
    button {
        attrs.onClickFunction = { setCount(count + 1) }
        +"$count"
    }
}

, :

useState

0

– Int

. , , (useState<String?>(null)

).
useState

, :
1. ( count
  
  Int
  
  );
2. ( setCount
  
  RSetState<Int> /* = (Int) -> Unit */
  
  ).
, setState

.

, count

, . , , , .

State .

: useState

– -. , , :

val counter = functionalComponent<RProps> {
    var count by useState(0)
    button {
        attrs.onClickFunction = { ++count }
        +"$count"
    }
}

Effect

, - – API WebSocket . , h3

:

val randomFact = functionalComponent<RProps> {
    val (randomFact, setRandomFact) = useState<String?>(null)
    useEffect(emptyList()) {
        GlobalScope.launch {
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}

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