Announcing Scala.js 1.0.0-M1
Announcing Scala.js 1.0.0-M1
Jul 3, 2017.
We are very excited to announce the first milestone of Scala.js 1.0.0, aka 1.0.0-M1!
This development release is mostly intended for testing purposes, and as a synchronization point with library authors so that they can start upgrading in preparation for the final release.
As the change in “major” version number witnesses, this release is not binary compatible with 0.6.x. Libraries need to be recompiled and republished using this milestone to be compatible.
Moreover, this release is not entirely source compatible with 0.6.x either. We expect, however, that further milestones for 1.0.0 will stay backward source compatible with this first milestone.
Please report any issues on GitHub.
The following libraries and testing frameworks have already been upgraded and published for 1.0.0-M1:
- scalajs-dom (static types for the DOM): 0.9.3
- scalajs-java-time: 0.2.2
- scalajs-java-logging: 0.1.2
- scalajs-jquery: 0.9.2
Preparations before upgrading from 0.6.x
Before upgrading to 1.0.0-M1, we strongly recommend that you upgrade to Scala.js 0.6.18, and address all deprecation warnings. Since Scala.js 1.0.0-M1 removes support for all the deprecated features in 0.6.x, it is easier to see the deprecation messages guiding you to the proper replacements.
Additionally to the explicitly deprecated things, make sure to use
scalaJSLinkerConfig instead of the following sbt settings:
Upgrade to 1.0.0-M1 from 0.6.18
As a first approximation, all you need to do is to update the version number in
In addition, if you use some of the components that have been moved to separate repositories, you will need to add some more dependencies in
If you use
jsDependencies (or rely on the
jsDependencies of your transitive dependencies):
addSbtPlugin("org.scala-js" % "sbt-jsdependencies" % "1.0.0-M1")in
If you use the Node.js with jsdom environment:
libraryDependencies += "org.scala-js" %% "scalajs-env-nodejs" % "1.0.0-M1"in
If you relied on the automatic selection of the above environment due to
jsDependencies += RuntimeDOM, you have to explicitly select it:
jsEnv := new org.scalajs.jsenv.jsdomnodejs.JSDOMNodeJSEnv()to the relevant Scala.js project settings
If you use the PhantomJS environment:
addSbtPlugin("org.scala-js" % "sbt-scalajs-env-phantomjs" % "1.0.0-M1")in
This should get your build up to speed to Scala.js 1.0.0-M1. From there, you should be able to test whether things go smoothly, or whether you are affected by the breaking changes detailed below.
This section discusses the backward incompatible changes, which might affect your project.
Access to the global scope instead of the global object
This is the only major breaking change at the language level.
In Scala.js 1.x,
Concretely, this has three consequences, which we outline below.
Further information can be found in the documentation about the global scope in Scala.js.
For example, the following is valid:
but the following variant, where the name
Math is only known at run-time, is not valid anymore:
Global scope objects cannot be stored in a separate
For example, the following is invalid and will cause a compile error:
as well as:
This follows from the previous rule. If the above two snippets were allowed, we could not check that we only access members with statically known names.
The first snippet can be advantageously replaced by a renaming import:
Accessing a member that is not declared causes a
ReferenceError to be thrown
This is a run-time behavior change, and in our experience the larger source of breakages in actual code.
Previously, reading a non-existent member of the global object, such as
would evaluate to
In Scala.js 1.x, this throws a
Similarly, writing to a non-existent member, such as
would previously create said global variable.
In Scala.js 1.x, it also throws a
A typical use case of the previous behavior was to test whether a global variable was defined or not, e.g.,
This idiom is broken in Scala.js 1.x, and needs to be replaced by an explicit use of
js.typeOf “method” is magical when its argument is member of a global scope object.
Consider the following object definition:
In 0.6.x, extending
js.JSApp has two consequences:
Foois recognized by the sbt plugin as a main object, and it can be used by
scalaJSUseMainModuleInitializer := true(as well as in deprecated launchers)
bar.Foo(), and its
main()method as well
In Scala.js 1.x, the second bullet is not true anymore, which constitutes a run-time behavior change.
If you need to preserve this behavior, you need to explicitly export
Foo and its
main() method as follows:
js.JSApp itself is deprecated, so you should use a
def main(args: Array[String]): Unit method instead.
js.JSApp will be removed in Scala.js 1.0.0-RC1.
js.UndefOr[A] is now an alias for
A | Unit
Instead of defining
js.UndefOr[+A] as its own type, it is now a simple type alias for
A | Unit:
Option-like API is of course preserved.
We do not expect this to cause any significant issue, but it may impact type inference in subtle ways that can cause compile errors for previously valid code.
You may have to adjust some uses of
js.UndefOr due to these changes, especially if using Scala 2.10.
testHtml replaces both
The separation of
testHtmlFullOpt, which were independent of the value of
scalaJSStage, caused significant unfixable issues in 0.6.x.
In Scala.js 1.x, both are replaced by a single task,
It is equivalent to the old
testHtmlFastOpt if the value of
FastOptStage (the default), and to
testHtmlFullOpt if it is
This makes it more consistent with other tasks such as
scalajs-javalib-ex was removed
scalajs-javalib-ex is removed in 1.x.
It only contained a partial implementation of
If you were using it, we recommend that you integrate a copy of its source code from Scala.js 0.6.x into your project.
js.use(x).as[T] was removed
The use cases for
js.use(x).as[T] have been dramatically reduced by non-native JS classes (previously known as Scala.js-defined JS classes).
This API seems virtually unused on the visible Web.
Moreover, it was the only macro in the Scala.js standard library.
We have therefore removed it from the standard library, and it is not provided anymore. On demand, we can republish it as a separate library, if you need it.
Scala 2.12.0 is not supported anymore
A severe regression in Scala 2.12.0 upstream, affecting
js.UndefOr, forced us to drop support for Scala 2.12.0.
Scala 2.12.1+ is supported.
There are very few enhancements in Scala.js 1.0.0-M1. Scala.js 1.0.0 is focused on simplifying Scala.js, not on adding new features. Nevertheless, here are a few enhancements.
Non-native JS classes by default (previously known as Scala.js-defined)
In Scala.js 0.6.x, we can declare a so-called Scala.js-defined JS class as follows:
In Scala.js 1.x, “Scala.js-defined” is the default, so the above snippet would be simply written as
Consequently, we also introduce a shift of terminology.
Such a class is now called a non-native JS class (by opposition to a native JS class with
Both native and non-native JS classes (resp. traits, objects) are called JS classes (resp. traits, objects).
All of them are called JS types.
Also note that the annotation
@ScalaJSDefined is deprecated, and will be removed in Scala.js 1.0.0-RC1.
Scala.js can access
require and other magical “global” variables of special JS environments
require in Node.js, are now visible to Scala.js.
For example, it is possible to dynamically call
require as follows in Scala.js 1.x:
We still recommend to use
CommonJSModule for statically known imports.
The sbt plugin builds on top of sbt-crossproject
Scala.js 0.6.x defined itself the notion of
crossProject and the
%%% operator for cross-platform dependencies.
In Scala.js 1.x, we standardize on sbt-crossproject, which provides a unified API that can also be used by Scala Native.
The changes are entirely backward source compatible, because
sbt-crossproject was designed with that specific goal.
However, the traditional cross-project constructor:
is now deprecated, as it hard-codes the JVM × JS pair of platforms. Instead, you should use
Amongst others, the following bugs have been fixed since 0.6.18:
- #2800 Global
classes cannot be accessed by Scala.js
- #2382 Name clash for
$outerpointers of two different nesting levels (fixed for Scala 2.10 and 2.11; 2.12 did not suffer from the bug in 0.6.x)
See the full list on GitHub.
Cross-building for Scala.js 0.6.x and 1.x
If you want to cross-compile your libraries for Scala.js 0.6.x and 1.x (which you definitely should), here are a couple tips.
Dynamically load a custom version of Scala.js
Since the version of Scala.js is not decided by an sbt setting in
build.sbt, but by the version of the sbt plugin in
project/plugins.sbt, standard cross-building setups based on
++ cannot be applied.
We recommend that you load the version of Scala.js from an environment variable.
For example, you can do this in your
You can then launch
from your command line to start up your build with Scala.js 1.0.0-M1.
Extra dependencies for JS environments
You can further build on the above
val scalaJSVersion to dynamically add dependencies on
scalajs-env-jsdom-nodejs if you use them:
In both cases, you can then use the source-compatible API in
build.sbt to select your JS environment of choice.
Extra dependencies for
The case of
sbt-jsdependencies is trickier, because it defines an
AutoPlugin that needs to be enabled on your projects.
This means that there is no source-compatible way to write your
The trick is to provide a fake
JSDependenciesPlugin when compiling for 0.6.x.
First add the following to
Then create a file
project/JSDependenciesCompat.scala with the following content:
You can now write
enablePlugins(JSDependenciesCompat) in your
build.sbt, and otherwise use
jsDependencies and other keys as usual.
Understanding how the trick works is left as an exercise for the reader.
Warning-free cross-compilation of
In Scala.js 1.x,
@ScalaJSDefined is deprecated because it is the default.
However, by default, in Scala.js 0.6.x, it is required.
Scala.js 0.6.17 introduced the compiler option
-P:scalajs:sjsDefinedByDefault to allow warning-free cross-compilation.
Add the following setting to your
And then remove all your
This will be source-compatible between both versions, and not produce any warnings.
Enabling sbt-crossproject even with Scala.js 0.6.x
This should only be necessary if your codebase also cross-compiles with Scala Native, in which case you need your build to depend on sbt-crossproject’s
sbt-scalajs-crossproject in the 0.6.x build.
However, you must not depend on it in the 1.x build, because it conflicts with the now built-in support of sbt-crossproject in Scala.js 1.x.
Therefore, here is what you should put in your
In that case, you still need to apply the shadowing import described in sbt-crossproject’s readme, i.e., in your