Web Components

With fritz2, you can easily use WebComponents in any html-context. Some of the following code-snippets are not runnable on their own. Please find the complete example here.

render {
div("weather-card") {
h2 { "Goslar" }
custom("m3-stars") {
attr("max", "5")
attr("current", "3.5")
}
// ...
}
}

Before you can use a custom element, you have to add the component to your site's scripts. One way is adding a script link pointing to the component which is hosted somewhere you can access it:

<script type="module" src="https://unpkg.com/@mat3e-ux/stars"></script>

If the component you want to use is published on npm, you can add it as a dependency in your Gradle-build:

dependencies {
implementation(kotlin("stdlib-js"))
// ...
implementation(npm("@mat3e-ux/stars"))
}

... and import it in your Kotlin-Code:

@JsModule("@mat3e-ux/stars")
@JsNonModule
abstract external class Stars : HTMLElement

Please see the official documentation for more details on this.

Depending on how the component is internally built, you might have to register it with the browser:

fun main() {
window.customElements.define("m3-stars", Stars::class.js.unsafeCast<() -> dynamic>())
// ...
}

For obvious reasons we cannot provide typesafe attributes for custom elements, but you can implement a Tag and provide an extension function for RenderContext:

class M3Stars(job: Job) : Tag<HTMLElement>("m3-stars", job = job), WithText<HTMLElement> {
fun max(value: Flow<Int>) = attr("max", value.asString())
fun current(value: Flow<Float>) = attr("current", value.asString())
}

fun RenderContext.m3Stars(content: M3Stars.() -> Unit): M3Stars = register(M3Stars(job), content)

Build a WebComponent

To build a WebComponent with fritz2, two steps are neccessary. First, implement your WebComponent-class:

object MyComponent : WebComponent<HTMLParagraphElement>() {
override fun RenderContext.init(element: HTMLElement, shadowRoot: ShadowRoot): HtmlTag<HTMLParagraphElement> {
return p {
+"I am a WebComponent"
}
}
}

Next, register your component:

fun main() {
registerWebComponent("my-component", MyComponent)
}

To observe one or more arguments, just add them to the registration:

registerWebComponent("my-component", MyComponent, "first-attr", "second-attr")

You can then use the values of these observed attributes in your init-method as a Flow:

val first = MyComponent.attributeChanges("first-attr")

render {
first.render { firstAttr ->
p { +firstAttr }
}
}

To react to the lifecycle of your component, you can override the according methods from the specification.

Packaging (i.e. as a npm-package) and publishing is out of scope of this documentation.

Again, to see it in action, please have a look at our webcomponents example.