Kilua

Composable web framework for Kotlin/Wasm and Kotlin/JS.

Kilua allows you to build modern web applications with the Kotlin language.

It is powered by the Compose Runtime and is similar to the compose-html library. It gives you clean, modular API to create declarative UI components and manage their state. Unlike compose-html, Kilua supports both Kotlin/Wasm and Kotlin/JS targets. It also provides a lot of ready to use components for many typical web application use cases.

Kilua is a kind of successor to my KVision framework. Writing Kilua applications should be familiar to both Compose users (@Composable functions, state management, coroutines/flow integration) and KVision users (component based API, allowing some imperative, direct ways to interact with the UI components).

Features

• Use powerful Compose programming model and state management to develop web applications.
• Choose from the wide range of ready to use components and form inputs.
• Compile the same application code for Kotlin/Wasm and Kotlin/JS targets.
• Create fullstack applications with Kilua RPC library.
• Translate your application to other languages with Gettext - one of the most widely used tool for i18n.
• Deploy your application with full SSR (Server Side Rendering) for better SEO performance and user experience.
• Export your application as a set of static HTML files for more affordable hosting solutions.

Project status

Kilua is being actively developed. Please create an issue for any bugs or feature requests. Contributions and PRs are welcomed. All artifacts are published to Maven Central.

Documentation and examples

The official guide is published at https://kilua.gitbook.io/kilua-guide. It's still a work in progress and may be incomplete.

Current API documentation is published at https://rjaros.github.io/kilua/api/.

Different example applications can be found in the examples directory, including fully compatible TodoMVC and Realworld.io (with SSR) implementations.

More documentation, including tutorials and guides, is planned for the future.

Building and running the examples

To build the examples, you need to have JDK 17 or later installed.

The following tasks are available from the root project level:

• ./gradlew -t :examples:[exampleName]:jsRun - run the webpack dev server in continuous build mode for JS target on http://localhost:3000
• ./gradlew -t :examples:[exampleName]:wasmJsRun - run the webpack dev server in continuous build mode for Wasm target on http://localhost:3000
• ./gradlew :examples:[exampleName]:jsBrowserDistribution - build production application for JS target to examples/[exampleName]/build/dist/js/productionExecutable directory
• ./gradlew :examples:[exampleName]:wasmJsBrowserDistribution - build production application for Wasm target to examples/[exampleName]/build/dist/wasmJs/productionExecutable directory

For fullstack and SSR examples additional tasks are available:

• ./gradlew :examples:[exampleName]:jvmRun - run the backend application for development on http://localhost:8080
• ./gradlew :examples:[exampleName]:jarWithJs - build and package the production application with JS frontend to examples/[exampleName]/build/libs directory
• ./gradlew :examples:[exampleName]:jarWithWasmJs - build and package the production application with Wasm frontend to examples/[exampleName]/build/libs directory
• ./gradlew :examples:[exampleName]:exportWithJs - export static site with JS frontend to examples/[exampleName]/build/site directory
• ./gradlew :examples:[exampleName]:exportWithWasmJs - export static site with Wasm frontend to examples/[exampleName]/build/site directory

To run packaged fullstack or SSR example just use java -jar [exampleName]-[version].jar command.

Note: use gradlew.bat instead of ./gradlew on Windows operating system.

If you want to start your own project, just copy the Kilua template project.

Code sample

This is a simple "Hello, world!" application written in Kilua:

import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import dev.kilua.Application
import dev.kilua.CoreModule
import dev.kilua.compose.root
import dev.kilua.html.button
import dev.kilua.html.div
import dev.kilua.html.unaryPlus
import dev.kilua.startApplication

class App : Application() {

    override fun start() {
        root("root") {
            var state by remember { mutableStateOf("Hello, world!") }

            div {
                +state
            }
            button("Add an exclamation mark") {
                onClick {
                    state += "!"
                }
            }
        }
    }
}

fun main() {
    startApplication(::App, CoreModule)
}

SSR (Server-Side Rendering)

Kilua is the first Kotlin/Wasm and Kotlin/JS web framework supporting true Server-Side Rendering. SSR is a crucial concept in modern web development that enhances user experience and boosts SEO performance. Kilua SSR support is based on the possibility to run exactly the same application code both in the browser and in NodeJs environment. What's more, you can easily use WASM compilation target for much better performance.

SSR Features

• Preparing application for SSR is as easy as changing the router class.
• Ability to use external API calls and fullstack RPC services.
• Automatically extracting CSS styles from JS bundle and injecting them into the HTML document before sending to the browser.
• Serialization of the application state from the server to the client side.

Current limitations

• The URL address and the browser preferred locale need to be the only source of the application state.
• Using browser APIs directly is not recommended.
• Advanced JS components (like RichText, Tabulator etc.) are rendered on the server as simple HTML placeholders.
• Rendering authenticated content is not supported at the moment.
• The "hydration" is implemented in a very primitive way (by replacing the rendered content).

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