sjrd / scalajs-reflect

Proof of concept of a "linker plugin" enabling some reflection for Scala.js

Version Matrix


Build Status Scala.js

scalajs-reflection is a combination of an sbt plugin and a run-time API enabling a controlled amount of run-time reflection in Scala.js projects.


Add the following line to your project/plugins.sbt file:

addSbtPlugin("be.doeraene" % "sbt-scalajs-reflection" % "0.1.1")

and the following settings to your build.sbt file:


libraryDependencies += "be.doeraene" %%% "scalajs-reflection" % "0.1.1"

In addition, you need to specify what classes will be reflectible, and what reflective operations will be enabled on them. To do so, use the scalaJSReflectSelectors setting. For example, to enable Reflect.getClassForName on all subclasses of some class or trait foo.Bar, use:

scalaJSReflectSelectors ++= Seq(
  selectDescendentClasses("foo.Bar") -> reflectClassByName()

Each element of the Seq must be a pair of an entity selector and a reflective operation. The operation will be enabled on all classes matched by the entity selector.

Available selectors are:

  • selectSingleClass("foo.Bar"): select exclusively foo.Bar
  • selectDescendentClasses("foo.Bar"): select foo.Bar and all its descendants

Note that, to select the class of a Scala object, you need to append a $ at the end of its full name, e.g., "foo.Bar$".

Available operations are:

  • reflectClassByName(): enables Reflect.getClassForName
  • reflectEnumerateClass() enables Reflect.enumerateClasses
  • reflectDeclaredConstructors(): enables Reflect.getDeclaredConstructors
  • reflectModuleAccessor(): enables Reflect.loadModule


  • be.doeraene.sjsreflect.Reflect
    • Reflect.getClassForName(fqcn: String): Class[_]: find a class by its name
    • Reflect.enumerateClasses: Array[Class[_]]: an array of the specified classes
    • Reflect.getDeclaredConstructors[T](clazz: Class[T]): Array[Constructor[T]]: lists the declared constructors of the given class
    • Reflect.loadModule[T](clazz: Class[T]): T: loads the module instance of the given module class (a Scala object)
  • be.doeraene.sjsreflect.Constructor[T]
    • ctor.getParameterTypes(): Array[Class[_]]: returns the list of the parameter types of the constructor
    • ctor.newInstance(actualArgs: Any*): T: invokes the constructor with the given arguments, and returns the created instance