JSApp

Old-style base class for top-level, entry point main objects.

JSApp provides two services to an object Foo that extends it. These two services are replaced by two different features, starting with Scala.js 0.6.18.

Discoverability by sbt as main object

Since Scala.js 0.6.18, the sbt plugin can recognize "standard" main methods of the form

def main(args: Array[String]): Unit = ...

in objects, even if they do not extend JSApp. Use such a main method to replace JSApp in the context of discoverability by sbt.

To enable it as main method, make sure you also set

scalaJSUseMainModuleInitializer := true

in your project settings.

Automatic export to JavaScript

Given

package bar

object Foo extends js.JSApp {
  def main(): Unit = println("Hello world!")
}

the object Foo and its main method are automatically exported such that JavaScript code can call

bar.Foo().main();

To achieve exactly the same behavior without JSApp, define Foo as

package bar

object Foo {
  @JSExportTopLevel("bar.Foo")
  protected def getInstance(): this.type = this

  @JSExport
  def main(): Unit = println("Hello world!")
}

Alternatively, you can define it as

package bar

object Foo {
  @JSExportTopLevel("bar.Foo.main")
  def main(): Unit = println("Hello world!")
}

but in that case, the JavaScript code will have to be changed to

bar.Foo.main()