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Announcing Scala.js 1.3.0.
Co-authored-by: Tobias Schlatter <[email protected]>
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‎_config.yml

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### VERSIONS ###
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versions:
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scalaJS: 1.2.0
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scalaJS: 1.3.0
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scalaJSBinary: 1
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scalaJS06x: 0.6.33
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scalaJS06xBinary: 0.6

‎_data/library/versions.yml

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- 1.0.0
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- 1.1.0
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- 1.2.0
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- 1.3.0

‎_posts/news/2020-10-16-announcing-scalajs-1.3.0.md

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---
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layout: post
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title: Announcing Scala.js 1.3.0
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category: news
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tags: [releases]
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permalink: /news/2020/10/16/announcing-scalajs-1.3.0/
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---
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We are excited to announce the release of Scala.js 1.3.0!
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This release brings one of the most awaited features for Scala.js: module splitting support!
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It is now possible to split the generated .js file into multiple modules, to optimize download size in multi-page applications or speed up incremental bundling.
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In addition, this release contains a number of new methods and classes in the JDK implementation, among which the higher-order methods of the `java.util` collections, and the locale-sensitive overloads of `String.toLowerCase`, `toUpperCase` and `format`.
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Read on for more details.
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<!--more-->
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## Getting started
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If you are new to Scala.js, head over to [the tutorial]({{ BASE_PATH }}/tutorial/).
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If you need help with anything related to Scala.js, you may find our community [on Gitter](https://gitter.im/scala-js/scala-js) and [on Stack Overflow](https://stackoverflow.com/questions/tagged/scala.js).
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Bug reports can be filed [on GitHub](https://github.com/scala-js/scala-js/issues).
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## Release notes
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If upgrading from Scala.js 0.6.x, make sure to read [the release notes of Scala.js 1.0.0]({{ BASE_PATH }}/news/2020/02/25/announcing-scalajs-1.0.0/) first, as they contain a host of important information, including breaking changes.
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This is a **minor** release:
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* It is backward binary compatible with all earlier versions in the 1.x series: libraries compiled with 1.0.x through 1.2.x can be used with 1.3.0 without change.
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* It is *not* forward binary compatible with 1.2.x: libraries compiled with 1.3.0 cannot be used with 1.2.x or earlier.
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* It is *not* entirely backward source compatible: it is not guaranteed that a codebase will compile *as is* when upgrading from 1.2.x (in particular in the presence of `-Xfatal-warnings`).
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As a reminder, libraries compiled with 0.6.x cannot be used with Scala.js 1.x; they must be republished with 1.x first.
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## Known source breaking changes
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### `js.Promise.then`
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The result type of `js.Promise.then` was changed from `js.Thenable` to `js.Promise`.
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This is unlikely to cause any issue in most cases, since `js.Promise` extends `js.Thenable`.
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It might cause compilation errors in some rare cases due to type inference, or if you declare a subclass of `js.Promise`.
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## Module splitting
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### Quickstart
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First, instead of `fastOptJS` / `fullOptJS`, use `fastLinkJS` / `fullLinkJS`.
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The outputs of those commands will be in a subdirectory like `project/target/scala-2.13/project-fastopt/`, instead of as a single file `.../scala-2.13/project-fastopt.js`.
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You can then create different entry points and/or generate as many small modules as possible using the following setups.
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#### For different entry points
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Set the `moduleID` for your top-level exports and/or module initializers explicitly (a module initializer is basically a main method for the module).
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The default `moduleID` is `"main"`.
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{% highlight scala %}
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@JSExportTopLevel(name = "startAdmin", moduleID = "admin")
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def startAdmin(): Unit = ???
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{% endhighlight %}
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{% highlight scala %}
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import org.scalajs.linker.interface.ModuleInitializer
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scalaJSModuleInitializers in Compile += {
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ModuleInitializer.mainMethod("my.app.admin.Main", "main")
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.withModuleID("admin")
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}
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{% endhighlight %}
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Everything with the same `moduleID` will go into the same entry point module.
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#### For many small modules
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By default, module splitting genereates as few modules as possible.
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In some cases, generates as many modules as small as possible is preferable, which can be configured with:
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{% highlight scala %}
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import org.scalajs.linker.interface.ModuleSplitStyle
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scalaJSLinkerConfig ~= (_.withModuleSplitStyle(ModuleSplitStyle.SmallestModules))
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{% endhighlight %}
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### What is Module Splitting?
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With module splitting, the Scala.js linker splits its output into multiple JavaScript modules (i.e. files).
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Both ES6 modules (`ModuleKind.ESModule`) and CommonJS modules (`ModuleKind.CommonJSModule`) are supported.
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There are several reasons to split JavaScript output into multiple files:
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* Share code between different parts of an application (e.g. user/admin interfaces).
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* Create smaller files to minimize changes for incremental downstream tooling.
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* Load parts of a large app progressively (not supported yet, see [#4201](https://github.com/scala-js/scala-js/issues/4201)).
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The Scala.js linker can split a full Scala.js application automatically based on:
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* The entry points (top-level exports and module initializers)
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* The split style (fewest modules or smallest modules)
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### Entry Points
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Scala.js-generated code has two different kinds of entry points:
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* Top level exports: Definitions to be called from external JS code.
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* Module initializers: Code that gets executed when a module is imported (i.e., main methods).
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The Scala.js linker determines how to group entry points into different (public) modules by using their assigned `moduleID`.
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The default `moduleID` is `"main"`.
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The `moduleID` of a top-level export can be specified using the `moduleID` parameter.
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The `moduleID` of a `ModuleInitializer` can be specified by the `withModuleID` method.
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**Example**:
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Say you have the following `App.scala` and `build.sbt`:
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{% highlight scala %}
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package my.app
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import scala.collection.mutable
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import scala.scalajs.js.annotation._
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// Separate objects to allow for splitting.
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object AppA {
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@JSExportTopLevel(name = "start", moduleID = "a")
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def a(): Unit = println("hello from a")
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}
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object AppB {
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private val x = mutable.Set.empty[String]
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@JSExportTopLevel(name = "start", moduleID = "b")
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def b(): Unit = {
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println("hello from b")
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println(x)
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}
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def main(): Unit = x.add("something")
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}
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{% endhighlight %}
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{% highlight scala %}
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import org.scalajs.linker.interface.ModuleInitializer
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scalaJSModuleInitializers in Compile += {
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ModuleInitializer.mainMethod("my.app.AppB", "main").withModuleID("b")
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}
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{% endhighlight %}
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This would generate two public modules `a.js` / `b.js`.
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`a.js` will export a method named `start` that calls `AppA.a`.
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`b.js` will export a method named `start` that calls `AppB.b`.
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Further, importing `b.js` will call `AppB.main`.
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Note that there is no public module `main.js`, because there is no entry point using the default `moduleID`.
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### Module Split Styles
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So far, we have seen how public modules can be configured.
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Based on the public modules, the Scala.js linker generates internal modules for the shared code between the public modules.
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Unlike public modules, internal modules may not be imported by user code.
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Doing so is undefined behavior and subject to change at any time.
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The linker generates internal modules automatically based on the dependency graph of the code and `moduleSplitStyle`.
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You can change it as follows:
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{% highlight scala %}
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import org.scalajs.linker.interface.ModuleSplitStyle
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scalaJSLinkerConfig ~= (_.withModuleSplitStyle(ModuleSplitStyle.SmallestModules))
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{% endhighlight %}
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There are currently two module split styles: `FewestModules` and `SmallestModules`.
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#### `FewestModules`
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Create as few modules as possible without including unnecessary code.
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This is the default.
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In the example above, this would generate:
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* `a.js`: public module, containing `AppA` and the export of `start`.
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* `b.js`: public module, containing `AppB`, `mutable.Set`, the export of `start` and the call to `AppB.main`
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* `a-b.js`: internal module, Scala.js core and the implementation of `println`.
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This also works for more than two public modules, creating intermediate shared (internal) modules as necessary.
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#### `SmallestModules`
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Create modules that are as small as possible.
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The smallest unit of splitting is a Scala class.
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Using this mode typically results in an internal module per class with the exception of classes that have circular dependencies: these are put into the same module to avoid a circular module dependency graph.
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In the example above, this would generate:
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* `a.js`: public module, containing the export of `start`.
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* `b.js`: public module, containing the export of `start` and the call to `AppB.main`
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* many internal small modules (~50 for this example), approximately one per class.
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Generating many small modules can be useful if the output of Scala.js is further processed by downstream JavaScript bundling tools.
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In incremental builds, they will not need to reprocess the entire Scala.js-generated .js file, but instead only the small modules that have changed.
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### Linker Output
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With module splitting, the set of files created by the linker is not known at invocation time.
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To support this new requirement, the linker output is configured as follows:
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* A directory where all files go: `scalaJSLinkerOutputDirectory`
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* Patterns for output file names: `outputPatterns` on `scalaJSLinkerConfig`.
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Both of these have reasonable defaults and usually do not need to be changed.
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The exception is file extensions.
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If you need to produce `*.mjs` files for Node.js, use:
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{% highlight scala %}
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import org.scalajs.linker.interface.OutputPatterns
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scalaJSLinkerConfig ~= (_.withOutputPatterns(OutputPatterns.fromJSFile("%s.mjs")))
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{% endhighlight %}
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In order to make sense of the files in the directory, linking returns a `Report` listing the public modules and their file names.
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### sbt backwards compatibility
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Since the `fastOptJS` / `fullOptJS` keys/tasks assume that linking will produce a single file, we had to introduce two new keys/tasks for linking: `fastLinkJS` / `fullLinkJS`.
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These tasks return the `Report` instead of an individual `File`.
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In order to ensure backwards compatibility, the `fastOptJS` / `fullOptJS` tasks now invoke `fastLinkJS` / `fullLinkJS` respectively and copy the produced files to their target location.
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However, this only works if the linker produced a single public module.
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So with actual module splitting, `fastOptJS` / `fullOptJS` will fail.
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The `run` and `test` tasks now depend on `fastLinkJS` / `fullLinkJS` (depending on the `scalaJSStage`) and load the public module with `moduleID="main"` (they fail if no such module exists).
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This does not change their behavior for existing builds but allows running and testing with module splitting enabled.
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## Miscellaneous
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### New JDK APIs
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This release contains a significant amount of additions in the JDK APIs that we support, notably thanks to contributions by [@er1c](https://github.com/er1c), [@ekrich](https://github.com/ekrich) and [@exoego](https://github.com/exoego).
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New interface definitions in `java.util.function.*`:
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* `BiConsumer`, `Supplier`, `Function`, `BiFunction`, `UnaryOperator`, `BinaryOperator` and `BiPredicate`
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* Specializations of `Supplier`, and `Predicate`
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New classes:
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* `java.lang.Character.UnicodeBlock`
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* `java.util.StringTokenizer`
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* `java.io.CharArrayWriter`
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* `java.io.CharArrayReader`
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Methods with fixed behavior to comply with the JDK specification:
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* In `java.lang.Character`:
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* `toLowerCase(Char)` and `toUpperCase(Char)`
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* In `java.lang.String`:
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* `compareTo`
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* `equalsIgnoreCase`
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* `compareToIgnoreCase`
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New methods in existing classes and interfaces (some are only available when compiling on a recent enough JDK):
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* In `java.lang.String`:
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* `repeat` (JDK 11+)
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* In `java.lang.Character`:
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* `toLowerCase(codePoint: Int)` and `toUpperCase(codePoint: Int)`
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* `toTitleCase(ch: Char)` and `toTitleCase(codePoint: Int)`
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* `highSurrogate` and `lowSurrogate`
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* `hashCode(ch: Char)`
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* `reverseBytes(ch: Char)`
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* `toString(codePoint: Int)` (JDK 11+)
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* Default methods in `java.util.Iterator`:
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* `remove`
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* `forEachRemaining`
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* Default methods in `java.util.List`:
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* `sort`
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* `replaceAll`
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* Default methods in `java.util.Map`:
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* `getOrDefault`
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* `forEach`
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* `replaceAll`
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* `putIfAbsent`
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* `remove(key, value)`
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* `replace(key, oldValue, newValue)`
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* `replace(key, value)`
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* `computeIfAbsent`
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* `computeIfPresent`
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* `compute`
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* `merge`
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* In `java.util.Optional`:
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* `isEmpty` (JDK 11+)
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* `ifPresent`
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* `ifPresentOrElse` (JDK 9+)
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* `filter`
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* `map`
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* `flatMap`
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* `or` (JDK 9+)
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* `orElse`
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* `orElseGet`
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* `orElseThrow(Supplier)`
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* `orElseThrow()` (JDK 10+)
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* In `java.util.Properties`:
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* `load`
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* `save`
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* `store`
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* `list`
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Finally, the following `Locale`-sensitive methods have been added, although they will only transitively link if support for `java.util.Locale` APIs is enabled using [scala-java-locales](https://github.com/cquiroz/scala-java-locales):
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* In `java.lang.String`:
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* `toLowerCase(Locale)` and `toUpperCase(Locale)`
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* `format(Locale, ...)`
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* In `java.util.Formatter`:
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* constructors with a `Locale` parameter
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* `format(Locale, ...)`
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Speaking of locales, we have slightly changed the definition of the default locale of Scala.js.
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Previously, it was specified as `en-US`.
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Starting from Scala.js 1.3.0, it is specified as `Locale.ROOT`.
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This change makes no difference in terms of behavior (only in terms of "spirit"), since all the methods that were previously implemented in Scala.js have the same behavior for `ROOT` than for `en-US`.
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Note that it is not possible to change the default locale, as methods that do not take `Locale` arguments are hard-coded for the behavior of `Locale.ROOT` (even when `scala-java-locales` is used).
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To get locale-sensitive behavior, the overloads taking explicit `Locale` arguments must be used.
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## Bug fixes
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Among others, the following bugs have been fixed in 1.3.0:
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* [#4195](https://github.com/scala-js/scala-js/issues/4195) `LinkedHashMap` iteration not empty after `clear`
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* [#4188](https://github.com/scala-js/scala-js/issues/4188) Make `js.Promise.then` return `js.Promise` instead of `js.Thenable`
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* [#4203](https://github.com/scala-js/scala-js/issues/4203) `Matcher.region` not mutating the matcher
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* [#4204](https://github.com/scala-js/scala-js/issues/4204) `Matcher.start()/end()` give incorrect results
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* [#4210](https://github.com/scala-js/scala-js/issues/4210) `java.util.Date.from(Instant)` throws the wrong kind of exception
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You can find the full list [on GitHub](https://github.com/scala-js/scala-js/issues?q=is%3Aissue+milestone%3Av1.3.0+is%3Aclosed).

‎assets/badges/scalajs-1.3.0.svg

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‎doc/all-api.md

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## All previous versions of the API
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### Scala.js 1.3.0
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* [1.3.0 scalajs-library]({{ site.production_url }}/api/scalajs-library/1.3.0/scala/scalajs/js/index.html)
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* [1.3.0 scalajs-test-interface]({{ site.production_url }}/api/scalajs-test-interface/1.3.0/)
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* [1.3.0 scalajs-ir]({{ site.production_url }}/api/scalajs-ir/1.3.0/org/scalajs/ir/index.html)
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* [1.3.0 scalajs-linker-interface]({{ site.production_url }}/api/scalajs-linker-interface/1.3.0/org/scalajs/linker/interface/index.html) ([Scala.js version]({{ site.production_url }}/api/scalajs-linker-interface-js/1.3.0/org/scalajs/linker/interface/index.html))
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* [1.3.0 scalajs-linker]({{ site.production_url }}/api/scalajs-linker/1.3.0/org/scalajs/linker/index.html) ([Scala.js version]({{ site.production_url }}/api/scalajs-linker-js/1.3.0/org/scalajs/linker/index.html))
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* [1.3.0 scalajs-test-adapter]({{ site.production_url }}/api/scalajs-sbt-test-adapter/1.3.0/org/scalajs/testing/adapter/index.html)
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* [1.3.0 sbt-scalajs]({{ site.production_url }}/api/sbt-scalajs/1.3.0/#org.scalajs.sbtplugin.package)
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### Scala.js 1.2.0
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* [1.2.0 scalajs-library]({{ site.production_url }}/api/scalajs-library/1.2.0/scala/scalajs/js/index.html)
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* [1.2.0 scalajs-test-interface]({{ site.production_url }}/api/scalajs-test-interface/1.2.0/)

‎doc/internals/version-history.md

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## Version history of Scala.js
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- [1.3.0](/news/2020/10/16/announcing-scalajs-1.3.0/)
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- [1.2.0](/news/2020/09/09/announcing-scalajs-1.2.0/)
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- [1.1.1](/news/2020/07/02/announcing-scalajs-1.1.1/)
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- [1.1.0](/news/2020/05/18/announcing-scalajs-1.1.0/)

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