Announcing Scala.js 1.12.0
Nov 23, 2022.
We are excited to announce the release of Scala.js 1.12.0!
This release brings a number of bug fixes and enhancements. The highlights are:
**, introduced in ECMAScript 2016.
- Checked exceptions for
The Scala standard library was upgraded to version 2.12.17 and 2.13.10.
Read on for more details.
If you are new to Scala.js, head over to the tutorial.
If you need help with anything related to Scala.js, you may find our community in
#scala-js on Discord and on Stack Overflow.
Bug reports can be filed on GitHub.
If upgrading from Scala.js 0.6.x, make sure to read the release notes of Scala.js 1.0.0 first, as they contain a host of important information, including breaking changes.
This is a minor release:
- It is backward binary compatible with all earlier versions in the 1.x series: libraries compiled with 1.0.x through 1.11.x can be used with 1.12.0 without change.
- It is not forward binary compatible with 1.11.x: libraries compiled with 1.12.0 cannot be used with 1.11.x or earlier.
- It is not entirely backward source compatible: it is not guaranteed that a codebase will compile as is when upgrading from 1.11.x (in particular in the presence of
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.
Enhancements with compatibility concerns
Checked exceptions for
As documented in the semantics of Scala.js,
NegativeArraySizeExceptions are Undefined Behavior in Scala.js, similarly to
Prior to Scala.js 1.12.0, we made no effort internally to provide decent error messages, or any other kind of checks.
Starting with this release, erroneous conditions leading to one of these two exceptions are checked in development (fastLink) mode.
They will be reported as
UndefinedBehaviorErrors in fastLink mode, and unchecked in fullLink mode.
In some rare situations, this may turn code that appeared to work into actively throwing an exception.
Like other checked behaviors, it is now possible to configure the linker so that these exceptions are compliant. In that case, they will be thrown as specified for the JVM, in both fastLink and fullLink. You may enable them with the following sbt settings:
This may have significant performance impact in fullLink, like other compliant behaviors.
** operator (see below for details).
If calling a method named
"**" was intended, the above should be rewritten to
For example, the facade for
Starting from Scala.js 1.12.0, such operator methods should be annotated with
@JSOperator, as follows:
A compiler warning will be emitted if the annotation is missing.
ECMAScript 2016 introduced the
a ** b computes
a raised to the power
b, and is applicable to
Before Scala.js 1.12.0, it was not possible to write Scala.js code calling that operator.
Scala.js 1.12.0 now supports it, through the definition of an
@JSOperator def **, as follows:
Without the annotation, a compiler warning will be emitted, and the definition will behave as a call to a method named
"**" instead, for backward compatibility.
If that is actually the intended semantics, the warning can be silenced with an explicit
The following bugs have been fixed in 1.12.0:
- #4739 Incorrect codegen for singleton case from Scala 3 enum in Scala 2.13 codebase
j.u.Arrays.equals(Array[AnyRef])doe not handle
- #4753 The optimizer thinks that
- #4755 The optimizer does not respect eval order of generic array get/set with nulls
You can find the full list on GitHub.