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‎_posts/news/2015-01-12-announcing-scalajs-0.6.0-RC1.md‎

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---
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layout: post
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title: Announcing Scala.js 0.6.0-RC1
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category: news
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tags: [releases]
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---
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{% include JB/setup %}
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We are excited to announce the first release candidate of Scala.js 0.6.0, aka 0.6.0-RC1!
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Unless there are blocking issues with this RC, or issues requiring binary incompatible changes, this version will become 0.6.0 final.
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Scala.js 0.6.0-RC1 is not forward nor backward binary compatible with M1/M2/M3.
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To upgrade from 0.6.0-Mx, simply change the version number.
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If you're upgrading from M1/M2, you might need to address some compilation errors regarding the `js` package, but it should be straightforward.
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Should you encounter any trouble, do not hesitate to ask.
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The rest of this announcement is cumulative with the changes introduced in the milestones, and is therefore written wrt. 0.5.6.
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<hr/>
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As the change in "major" version number witnesses, this release is *not* binary compatible with 0.5.x.
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Libraries need to be recompiled and republished using 0.6.0-RC1 to be compatible.
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More importantly, this release is not source compatible with 0.5.x either.
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Please report any issues [on GitHub](https://github.com/scala-js/scala-js/issues).
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The following libraries and testing frameworks have already been upgraded and published for 0.6.0-RC1:
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* [DOM types](https://github.com/scala-js/scala-js-dom): `"org.scala-js" %%% "scalajs-dom" % "0.7.0"`
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* [jQuery types](https://github.com/scala-js/scala-js-jquery): `"be.doeraene" %%% "scalajs-jquery" % "0.7.0"`
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* [Scala.rx](https://github.com/lihaoyi/scala.rx): `"com.lihaoyi" %%% "scalarx" % "0.2.7-RC1"`
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* [ScalaTags](https://github.com/lihaoyi/scalatags): `"com.lihaoyi" %%% "scalatags" % "0.4.3-RC1"`
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* [Autowire](https://github.com/lihaoyi/autowire): `"com.lihaoyi" %%% "autowire" % "0.2.4-RC1"`
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* [µPickle](https://github.com/lihaoyi/upickle): `"com.lihaoyi" %%% "upickle" % "0.2.6-RC1"`
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* [µTest](https://github.com/lihaoyi/utest): `"com.lihaoyi" %%% "utest" % "0.2.5-RC1" % "test"`
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## Preparations before upgrading from 0.5.x
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### Upgrade to 0.5.6 if not already done
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Before upgrading to 0.6.0-RC1, **we strongly recommend that you upgrade to Scala.js 0.5.6**, and address all deprecation warnings.
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Scala.js 0.5.6 contains warnings for the most vicious breaking changes of 0.6.x.
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### Migrate away from the Jasmine test framework
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If you use the Jasmine test framework, migrate away from it to one of the other testing frameworks for Scala.js.
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The Jasmine test framework is *not* a good testing framework for Scala.js code, and is being *removed* in 0.6.x.
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Possible replacements:
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* [uTest](https://github.com/lihaoyi/utest)
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* [Little Spec](https://github.com/eecolor/little-spec)
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* [otest](https://github.com/cgta/otest)
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* [MiniTest](https://github.com/monifu/minitest)
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Note that these testing frameworks also need to upgrade to 0.6.0-RC1 before you can use them.
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## Upgrade to 0.6.0-RC1 from 0.5.6
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Basically, you need to apply the same kind of changes to your build files as in [this commit](https://github.com/sjrd/scala-js-example-app/commit/77d5f970267247c714a164f3dd72e51605f3ef66), which mostly consists in:
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* Upgrade to sbt >= 0.13.6 (the current version is 0.13.7).
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* Adaptations to new groupId and artifact names for Scala.js packages.
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* Adaptation to the new `AutoPlugin` infrastructure of the sbt plugin.
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* Drop the prefix `ScalaJSKeys.` for Scala.js-specific sbt keys, as they are not needed anymore.
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* Upgrade to 0.6.0-RC1-enabled versions of your dependencies.
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On the sbt command line, not much changes, except the way you use the `fastOpt` and `fullOpt` mode.
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In Scala 0.5.x, you could run in `fastOpt` mode with:
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> fastOptStage::run
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In 0.6.x, the mode is regulated by the setting `scalaJSStage`, which is one of:
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* `PreLinkStage` (default): uses Rhino
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* `FastOptStage`: `fastOpt` mode, uses Node.js or PhantomJS
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* `FullOptStage`: `fullOpt` mode, uses Node.js or PhantomJS
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You can change it from the command line with
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> set scalaJSStage := FastOptStage
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> run # runs in fastOpt mode
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In a multi-project build, you'll want to change it for all projects, which can be done with `in Global`:
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> set scalaJSStage in Global := FastOptStage
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## Major changes
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This section discusses major changes affecting source compatibility, which may or may not apply to your project.
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### `ClassCastException` becomes an undefined behavior
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The JVM, in its incommensurable magnanimity, throws nicely specified exceptions when you do something bad with your code.
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For example, it will nicely throw a `ClassCastException` if you perform an invalid `.asInstanceOf`, or an `ArithmeticException` if you divide an integer by 0.
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Since the beginning of time, Scala.js has handled most of these things as *undefined behavior*, i.e., *anything can happen* if these cases happen.
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Until 0.5.x, `ClassCastException`s were properly reported, though.
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We have found, however, that checking these buggy cases costs up to 100% overhead to the overall execution time of a Scala.js program.
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In Scala.js 0.6.x, therefore, invalid casts become an undefined behavior as well.
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However, the compiler will *still* be nice with you *in fastOpt mode*, by throwing an `UndefinedBehaviorError` if you perform an invalid cast (instead of a `ClassCastException`).
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`UndefinedBehaviorError` is a *fatal* error, meaning it won't be caught by `case NonFatal(e)` handlers.
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In fullOpt mode, the checks are removed for maximum efficiency.
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You *must not catch* `UndefinedBehaviorError`, since that would cause your program to behave differently in fastOpt mode than in fullOpt.
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The idea of `UndefinedBehaviorError` is that you can enjoy strict checks and stack traces while developing.
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If you really want `ClassCastException`s to be thrown reliably (both in fastOpt and fullOpt modes), you can enable them in your application, at the expense of runtime performance, with the following sbt setting:
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{% highlight scala %}
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scalaJSSemantics ~= { _.withAsInstanceOfs(org.scalajs.core.tools.sem.CheckedBehavior.Compliant) }
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{% endhighlight %}
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This applies to the entire application, including dependencies.
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There is no way to select parts of the application where this applies, because there is no way to make that sensical.
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### The `scala.scalajs.js` package has been simplified
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We have removed a lot of historical warts from the `scala.scalajs.js` package, mostly types and APIs with equivalents among normal Scala types and libraries:
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* `js.String`, `js.Boolean`, `js.Number` and `js.Undefined` have been removed, as well as their `js.prim.*` equivalent.
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`String`, `Boolean`, `Double` and `Unit` should be used instead.
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* `js.parseInt(s)` and `js.parseFloat(s)` should be replaced by `s.toInt` and `s.toDouble`.
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* `js.NaN`, `js.Infinity` should be replaced by `Double.NaN` and `Double.PositiveInfinity`.
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* `js.isNaN(x)` should be replaced by `x.isNaN`.
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* `js.isFinite(x)` should be replaced by `!x.isNaN && !x.isInfinite`.
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Methods provided by ECMAScript 5.1 on primitive strings and numbers can be enabled by importing the following implicit conversions:
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{% highlight scala %}
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import js.JSStringOps._
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import js.JSNumberOps._
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{% endhighlight %}
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### `js.native` in facade types
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When writing facade types, it was previously recommended to use `???` as a fake body for fields and methods.
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You should now use `js.native` instead, as in:
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{% highlight scala %}
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trait Foo extends js.Object {
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var bar: Int = js.native
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def foobar(x: Int): String = js.native
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}
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{% endhighlight %}
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The compiler will emit a warning if you use any other body.
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The warning will become an error in 1.0.0.
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### `@JSExport` exports to fully qualified names by default
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As announced by deprecation warnings in the 0.5.6 compiler, putting `@JSExport` without an explicit name on an `object` or `class` changes meaning between 0.5.x and 0.6.x.
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Consider this code:
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{% highlight scala %}
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package babar
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@JSExport
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class Foo
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{% endhighlight %}
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In 0.5.x, `Foo` is exported as `Foo`.
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In 0.6.x, it is exported as `babar.Foo` instead.
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### Testing frameworks adaptations
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If you are not a testing framework implementor, this section does not apply to you.
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Please follow the migration guidelines of any testing framework you may use.
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Until 0.5.x, Scala.js had a custom, ad-hoc substitute for the sbt testing interface, which allows testing frameworks to integrate with sbt.
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Although quite good in its own right, it suffered from several limitations, including the inability for one project to use more than one testing framework at the same time.
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Scala.js 0.6.x now supports its JS version of the original sbt testing interface, with all its power, API, and usability features.
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We also offer tools to make your testing framework fully source-compatible with the JVM and JS variants of the testing interface, without a single line of platform-specific source code.
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An existing barebone cross-compiling testing framework can be found [in our tests](https://github.com/scala-js/scala-js/tree/v0.6.0-RC1/sbt-plugin-test).
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Some highlights:
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* [Build definition for the cross-compiling framework](https://github.com/scala-js/scala-js/blob/v0.6.0-RC1/sbt-plugin-test/build.sbt#L49-L64)
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* [(Cross-compiling) source code of the testing framework](https://github.com/scala-js/scala-js/tree/v0.6.0-RC1/sbt-plugin-test/testFramework/src/main/scala/sbttest/framework)
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* [Build definition for a cross-compiling project using the framework](https://github.com/scala-js/scala-js/blob/v0.6.0-RC1/sbt-plugin-test/build.sbt#L66-L86)
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* [Source code of the project using the framework](https://github.com/scala-js/scala-js/tree/v0.6.0-RC1/sbt-plugin-test/multiTest)
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Adapting your testing framework to follow this structure is likely to be the easiest path of migration.
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You may also want to take a look at [the PR we made to uTest](https://github.com/lihaoyi/utest/pull/45) to migrate to Scala.js 0.6.x.
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Should you run into trouble, don't hesitate to ask on the mailing list!
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## Enhancements
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### <a name="cross-project"></a> Defining cross-compiling projects with `crossProject`
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When writing cross-compiling code, we need to have two separate projects in sbt for the JVM target and the JS target.
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The new `CrossProject` type, and its `crossProject` builder, helps in defining these pairs of projects in a DRY way.
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See the [documentation of `CrossProject`]({{ BASE_PATH }}/api/sbt-scalajs/0.6.0-RC1/#org.scalajs.sbtplugin.cross.CrossProject) for more information and examples.
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### Faster!
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Scala.js 0.6.x benefits from many performance improvements, most notably:
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* `asInstanceOf`s are unchecked (see above), giving `fullOpt` code up to twice as fast as before
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* `Range.foreach`, aka the `for (i <- 0 until n)` kind of loops, is inlined away, giving the same performance as an explicit `while` loop.
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* Higher-order operations on `js.Array`s and `js.Dictionary`s (such as `foreach`, `map`, etc.) are inlined away as `while` loops.
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* Various improvements to the optimizer.
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### Scala collection API for `js.Array[A]` and `js.Dictionary[A]`
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The title says it all: `js.Array[A]` and `js.Dictionary[A]` receive the entire Scala collection API, respectively of `mutable.Buffer[A]` and `mutable.Map[String, A]`.
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`js.Array` becomes the default implementation of `mutable.Buffer`, i.e., `mutable.Buffer.empty` returns a `js.Array` wrapped in a `js.WrappedArray`.
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### Implicits to make "writing JavaScript" easier
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Sometimes, for example when porting existing JavaScript code, we want to just "write JavaScript" inside our Scala.js code.
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A new object `js.DynamicImplicits` ([API]({{ BASE_PATH }}/api/scalajs-library/0.6.0-RC1/#scala.scalajs.js.DynamicImplicits$) provides implicit conversions that allow to write dynamically typed JavaScriptish code directly in Scala.js with a mimimal amount of boilerplate.
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Needless to say, these implicits should be handled with care, but they can come in handy.
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### On-demand strict floats
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Scala.js under-specifies `Float` operations by default, saying that they can sometimes behave as if they were `Double`s.
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In 0.6.x, you can configure your application to use *strict-float semantics*, guaranteeing that all `Float` operations behave as on the JVM, with the appropriate truncation of precision (with the notable exception of `.toString()`).
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The following sbt setting enables this:
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{% highlight scala %}
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scalaJSSemantics ~= { _.withStrictFloats(true) }
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{% endhighlight %}
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Beware that this can have a major impact on performance on VMs that do not support the [`Math.fround`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/fround) function.
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### Obfuscation of class names
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The `scalaJSSemantics` option also allows to obfuscate or otherwise rename the class names in the emitted .js file, as was requested in [#1113](https://github.com/scala-js/scala-js/issues/1113).
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For example, this sbt setting empties out all class names in the package `my.company`:
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{% highlight scala %}
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scalaJSSemantics ~= (_.withRuntimeClassName { linkedClass =>
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val fullName = linkedClass.fullName
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if (fullName.startsWith("my.company.")) ""
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else fullName
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})
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{% endhighlight %}
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This changes the value returned by `x.getClass.getName` or `classOf[C].getName`.
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### We publish to Maven Central
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This should probably not affect sbt users, but it now becomes possible to imagine a Maven plugin for Scala.js.
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To this effect, the sbt plugin codebase has also been refactored, and all parts that are not strictly bound to sbt as a build tool have been extracted in Mavenized artifacts.
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An enthusiast Maven user could therefore build a Maven plugin with relatively few lines of code.
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As a measurable figure, the code specific to sbt contains only 1,686 lines of code.
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## Bugfixes
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Amongst others, the following bugs have been fixed since 0.5.6:
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* [#1430](https://github.com/scala-js/scala-js/issues/1430) `ClassTag.unapply` method (for deconstruction) fails for raw JS classes
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* [#1423](https://github.com/scala-js/scala-js/issues/1423) String.getBytes returns trailing zeroes
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* [#1324](https://github.com/scala-js/scala-js/issues/1324) Date.parse should return a Double, not an Int
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* [#1349](https://github.com/scala-js/scala-js/issues/1349) Auto-completion in runMain task does not work
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* [#1192](https://github.com/scala-js/scala-js/issues/1192) hashCode for floating points has a very bad distribution
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* [#1402](https://github.com/scala-js/scala-js/issues/1402) `Traversers` does not handle the case of `Debugger`

‎doc/index.md‎

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### Scala.js
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#### Scala.js 0.6.0-RC1
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* [0.6.0-RC1 scalajs-library]({{ BASE_PATH }}/api/scalajs-library/0.6.0-RC1/#scala.scalajs.js.package)
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* [0.6.6-RC1 scalajs-test-interface]({{ BASE_PATH }}/api/scalajs-test-interface/0.6.0-RC1/)
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* [0.6.0-RC1 scalajs-stubs]({{ BASE_PATH }}/api/scalajs-stubs/0.6.0-RC1/)
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* [0.6.0-RC1 scalajs-ir]({{ BASE_PATH }}/api/scalajs-ir/0.6.0-RC1/#org.scalajs.core.ir.package)
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* [0.6.0-RC1 scalajs-tools]({{ BASE_PATH }}/api/scalajs-tools/0.6.0-RC1/#org.scalajs.core.tools.package) ([Scala.js version]({{ BASE_PATH }}/api/scalajs-tools-js/0.6.0-RC1/#org.scalajs.core.tools.package))
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* [0.6.0-RC1 scalajs-js-envs]({{ BASE_PATH }}/api/scalajs-js-envs/0.6.0-RC1/#org.scalajs.jsenv.package)
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* [0.6.0-RC1 scalajs-test-adapter]({{ BASE_PATH }}/api/scalajs-sbt-test-adapter/0.6.0-RC1/#org.scalajs.testadapter.package)
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* [0.6.0-RC1 sbt-scalajs]({{ BASE_PATH }}/api/sbt-scalajs/0.6.0-RC1/#org.scalajs.sbtplugin.package)
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#### Scala.js 0.6.0-M3
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* [0.6.0-M3 scalajs-library]({{ BASE_PATH }}/api/scalajs-library/0.6.0-M3/#scala.scalajs.js.package)
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* [0.6.6-M3 scalajs-test-interface]({{ BASE_PATH }}/api/scalajs-test-interface/0.6.0-M3/)
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* [0.6.0-M3 scalajs-stubs]({{ BASE_PATH }}/api/scalajs-stubs/0.6.0-M3/)
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* [0.6.0-M3 scalajs-ir]({{ BASE_PATH }}/api/scalajs-ir/0.6.0-M2/#org.scalajs.core.ir.package)
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* [0.6.0-M3 scalajs-ir]({{ BASE_PATH }}/api/scalajs-ir/0.6.0-M3/#org.scalajs.core.ir.package)
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* [0.6.0-M3 scalajs-tools]({{ BASE_PATH }}/api/scalajs-tools/0.6.0-M3/#org.scalajs.core.tools.package) ([Scala.js version]({{ BASE_PATH }}/api/scalajs-tools-js/0.6.0-M3/#org.scalajs.core.tools.package))
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* [0.6.0-M3 scalajs-js-envs]({{ BASE_PATH }}/api/scalajs-js-envs/0.6.0-M3/#org.scalajs.jsenv.package)
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* [0.6.0-M3 scalajs-test-adapter]({{ BASE_PATH }}/api/scalajs-test-adapter/0.6.0-M3/#org.scalajs.testadapter.package)

‎downloads.md‎

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The CLI distribution requires `scala` and `scalac` (of the right major version) to be on the execution path. Unpack it wherever you like and add the `bin/` folder to your execution path.
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#### Scala.js 0.6.0-RC1
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* [0.6.0-RC1, Scala 2.11 (tgz, 20MB)]({{ BASE_PATH }}/files/scalajs_2.11-0.6.0-RC1.tgz)
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* [0.6.0-RC1, Scala 2.11 (zip, 20MB)]({{ BASE_PATH }}/files/scalajs_2.11-0.6.0-RC1.zip)
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* [0.6.0-RC1, Scala 2.10 (tgz, 18MB)]({{ BASE_PATH }}/files/scalajs_2.10-0.6.0-RC1.tgz)
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* [0.6.0-RC1, Scala 2.10 (zip, 18MB)]({{ BASE_PATH }}/files/scalajs_2.10-0.6.0-RC1.zip)
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#### Scala.js 0.6.0-M3
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* [0.6.0-M3, Scala 2.11 (tgz, 18MB)]({{ BASE_PATH }}/files/scalajs_2.11-0.6.0-M3.tgz)
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* [0.6.0-M3, Scala 2.11 (zip, 18MB)]({{ BASE_PATH }}/files/scalajs_2.11-0.6.0-M3.zip)

‎index.md‎

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## Version History
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- [0.6.0-RC1](/news/2015/01/12/announcing-scalajs-0.6.0-RC1/)
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- [0.6.0-M3](/news/2014/12/22/announcing-scalajs-0.6.0-M3/)
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- [0.6.0-M2](/news/2014/12/05/announcing-scalajs-0.6.0-M2/)
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- [0.6.0-M1](/news/2014/12/01/announcing-scalajs-0.6.0-M1/)

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