IOWebApp is a convenient way to define the entry point to your web application. It is the analog to Cats Effect IOApp for the browser.

import calico.*
import{*, given}
import cats.effect.*
import fs2.dom.*

object MyCalicoApp extends IOWebApp:
  def render: Resource[IO, HtmlElement[IO]] =
    div("Toto, I've a feeling we're not in Kansas anymore.")

Your build.sbt should include:

scalaJSUseMainModuleInitializer := true

And your index.html should look something like this:

    <div id="app"></div>
    <script src="main.js"></script>

You can customize the id of your application’s root element.

override def rootElementId = "somewhere-over-the-rainbow"

IOWebApp also provides a window: fs2.dom.Window[IO] to access various Web APIs.

def render =
  window.location.href.get.toResource.flatMap { location =>
    div(s"Welcome to $location")