compose-multiplatform/examples/web-compose-in-js

How to use HTML based @Composable functions in JS?

Useful links:

• Use Kotlin Code from JS
• JavaScript modules
• webpack bundling

1. @Composable functions can't be invoked from JS directly (because every @Composable function has implicit parameters added by compiler plugin)
2. We can wrap @Composable functions into some usual function (with @JsExport) which can be invoked in JS as is.
3. Every call to a "wrapping" function will create a composition (part of DOM controlled by Compose runtime)
4. It's important to dispose a composition when it's not needed.
5. The composition's state can be controlled by creating an arbitrary Controller class, which implements and exposes necessary functions for state updates.

Simplified example (see full example in src/jsMain):

// Composables.kt

@JsExport
abstract class ComposeCounterAppController {
    abstract fun setCount(newCount: Int)
    abstract fun dispose()
}

@JsExport
fun ComposeCounterApp(rootId: String, onCountChange: (Int) -> Unit = {}): ComposeCounterAppController {
    var count: Int by mutableStateOf(0)

    val composition = renderComposable(rootElementId = rootId) {
        // Counter is a @Composable function
        // see full example in src/jsMain
        Counter(count) {
            count = it
            onCountChange(count)
        }
    }

    return object : ComposeCounterAppController() {
        override fun setCount(newCount: Int) {
            count = newCount
        }

        override fun dispose() {
            composition.dispose()
        }
    }
}

Then in JS we can use ComposeCounterApp function:

// see src/jsMain/resources/use_compose.js file for a full example

counterController = MyComposables.ComposeCounterApp('counterByCompose', (newCount) => {
    console.log(`Counter was updated. New value = ${newCount}`);
});

The module name was overridden to make it convenient for usage in JS:

// webpack.config.d/configModuleName.js

config.output = config.output || {};
config.output.library = "MyComposables";

Building and using the output

./gradlew jsBrowserProductionWebpack

This will produce the output in build/distributions. Then we can use exported functions from web-compose-in-js.js (the filename is defined by the project/module name).

<script src="web-compose-in-js.js"></script>
<script src="use_compose.js"></script>