# Events handling in Compose Web

**The API is experimental, and breaking changes can be expected**

You can add event listeners in the `attrs` block:

#### onClick
``` kotlin
Button(
    attrs = {
        onClick { wrappedMouseEvent -> 
            // wrappedMouseEvent is of `WrappedMouseEvent` type    
            println("button clicked at ${wrappedMouseEvent.movementX}, ${wrappedMouseEvent.movementY}")
            
            val nativeEvent = wrappedMouseEvent.nativeEvent // [MouseEvent](https://developer.mozilla.org/en/docs/Web/API/MouseEvent)
        }
    }
) {
    Text("Button")
}
```

#### onInput
``` kotlin
val text = remember { mutableStateOf("") }

TextArea(
    value = text.value,
    attrs = {
        onTextInput { wrappedTextInputEvent ->
            // wrappedTextInputEvent is of `WrappedTextInputEvent` type
            text.value = wrappedTextInputEvent.inputValue
        }
    }
)
```


#### Other event handlers

For events that don't have their own configuration functions in the `attrs` block, you can use `addEventListener` with the `name` of the event, `options`, and an pass an `eventListener` which receives a `WrappedEvent`. In this example, we're defining the behavior of a `Form` element when it triggers the `submit` event:

``` kotlin
Form(attrs = {
    this.addEventListener("submit") {
        console.log("Hello, Submit!")
        it.nativeEvent.preventDefault()
    }
})
```

Your event handlers receive wrapped events that inherit from `GenericWrappedEvent`, which also provides access to the underlying `nativeEvent` – the actual event created by JS runtime -
https://developer.mozilla.org/en-US/docs/Web/API/Event


There are more event listeners supported out of a box. We plan to add the documentation for them later on. In the meantime, you can find all supported event listeners in the [source code](https://github.com/JetBrains/androidx/blob/compose-web-main/compose/web/src/jsMain/kotlin/androidx/compose/web/attributes/EventsListenerBuilder.kt).


### Runnable example

```kotlin
import androidx.compose.runtime.*
import org.jetbrains.compose.web.css.*
import org.jetbrains.compose.web.dom.*
import org.jetbrains.compose.web.renderComposable

fun main() {
    renderComposable(rootElementId = "root") {
        Button(
            attrs = {
                onClick { wrappedMouseEvent ->
                    // wrappedMouseEvent is of `WrappedMouseEvent` type
                    println("button clicked at ${wrappedMouseEvent.movementX}, ${wrappedMouseEvent.movementY}")

                    val nativeEvent = wrappedMouseEvent.nativeEvent
                }
            }
        ) {
            Text("Button")
        }

        val text = remember { mutableStateOf("") }

        TextArea(
            value = text.value,
            attrs = {
                onTextInput { wrappedTextInputEvent ->
                    // wrappedTextInputEvent is of `WrappedTextInputEvent` type
                    text.value = wrappedTextInputEvent.inputValue
                }
            }
        )

        Span {
            Text("Typed text = ${text.value}")
        }
    }
}
```