Announcing Scala.js 0.6.17

Announcing Scala.js 0.6.17

Jun 4, 2017.

We are excited to announce the release of Scala.js 0.6.17!

This release is mostly a bug-fix release, but it also brings a few new features.

One bug fix which we would like to highlight is #2943/#2827. The optimizer exposed a quadratic behavior which meant insanely long times of fastOptJS on some codebases, which we have now fixed. This was particularly true in test suites using ScalaTest.

The main new feature of this release is the ability for facade libraries to support both the traditional NoModule style, where JS libraries are exposed as global variables and accessed through @JSGlobal, and the CommonJSModule style, where JS libraries are imported through @JSImport.

Read on for more details.

Getting started

If you are new to Scala.js, head over to the tutorial.

Release notes

If upgrading from Scala.js 0.6.14 or earlier, make sure to read the release notes of 0.6.15, which contain important migration information.

As a minor release, 0.6.17 is backward source and binary compatible with previous releases in the 0.6.x series. Libraries compiled with earlier versions can be used with 0.6.17 without change. However, it is not forward compatible: libraries compiled with 0.6.17 cannot be used by projects using 0.6.{0-16}.

Please report any issues on GitHub.

New features

Double support for global variables/imports in facade types

Since Scala.js 0.6.13, Scala.js codebases have had the option to emit CommonJS modules, using the CommonJSModule module kind. In that mode, JS libraries are imported through facade types with @JSImport. For example, one might import jQuery as

@js.native
@JSImport("jquery.js", JSImport.Default)
object JQuery extends js.Object {
  def apply(selector: String): JQuery = js.native
}

However, if one uses the more traditional “script” style (with the NoModule module kind), where JS libraries are exposed as global variables, the facade would have to look like the following:

@js.native
@JSGlobal("$")
object JQuery extends js.Object {
  def apply(selector: String): JQuery = js.native
}

This means that there was no way to write a facade library that works both for applications using NoModule and CommonJSModule.

In Scala.js 0.6.17, the facade can now be declared as follows to support both module kinds:

@js.native
@JSImport("jquery.js", JSImport.Default, globalFallback = "$")
object JQuery extends js.Object {
  def apply(selector: String): JQuery = js.native
}

When linking with scalaJSModuleKind := ModuleKind.CommonJSModule, this will behave as in the first example. When linking with ModuleKind.NoModule, the globalFallback is used, and the facade behaves as in the second example with @JSGlobal("$").

Opt-in @ScalaJSDefined by default

As a sneak peak of Scala.js 1.x, you can now opt-in for @ScalaJSDefined by default in your codebase.

As you might know, in Scala.js 1.x, classes, traits and objects extending js.Any will be “Scala.js-defined” by default. In 0.6.x, the compiler forces you to choose between @js.native and @ScalaJSDefined with warnings. In 1.x however, the @ScalaJSDefined annotation will be deprecated and have no effect.

In other words, when migrating from 0.6.x to 1.x, a class such as

@ScalaJSDefined
class Foo extends js.Object {
  def bar(x: Int): Int = x + 1
}

will have to lose its annotation and simply become

class Foo extends js.Object {
  def bar(x: Int): Int = x + 1
}

In Scala.js 0.6.17, you can opt-in to the new behavior of Scala.js 1.x. To do so, give the option -P:scalajs:sjsDefinedByDefault to the Scala compiler. In sbt, you can do so with:

// For a Scala.js-only project
lazy val foo = project.
  enablePlugins(ScalaJSPlugin).
  settings(
    ...
    scalacOptions += "-P:scalajs:sjsDefinedByDefault"
  )

// For a cross project:
lazy val bar = crossProject.
  settings(
    ...
  ).
  jsSettings(
    ...
    scalacOptions += "-P:scalajs:sjsDefinedByDefault"
  )

With this compiler option, you can safely remove all your @ScalaJSDefined annotations, and benefit from the cleaner syntax of Scala.js 1.x today!

Codebases with and without the option are still interoperable between each other. Using the option does not prevent you from depending on libraries that do not use it, nor does it prevent codebases not using it from depending on your library.

Bug fixes

Among others, the following bugs have been fixed in 0.6.17:

  • #2943 Performance regression in the optimiser
  • #2827 Slow incremental linking times for fastOptJS (with ScalaTest)
  • #2979 %%% does not work in JVM projects
  • #2953 Type-matching arbitrary things against Byte/Short/Int ends up calling toString
  • #2928 return x match {...} crashes the compiler
  • #2927 JUnit assertEquals(_: Double, _: Double) not failing for JS, only for JVM
  • #2845 Scala.js compiler doesn’t pass through UTF-8 correctly for dependencies
  • #2798 Allow the sbt plugin to work if run on Java 9 (the optimizer will not be parallel)
  • #2786 Code which runs with fastOptJS but crashes with fullOptJS

You can find the full list on GitHub.