Generic way of array creation in Scala.js

Question

I'm looking for a generic way of array creation in Scala.js.

The following code works fine in JVM and Scala Native platforms:

def newArray[A](fqcn: String, size: Int): Array[A] = {
  val clazz = Class.forName(fqcn)
  java.lang.reflect.Array.newInstance(clazz, size).asInstanceOf[Array[A]]
}

But in Scala.js I cannot find an ability to create an instance of java.lang.Class.

I've tried such replacement for Class.forName but it doesn't work for arbitrary classes:

val clazz = scala.scalajs.reflect.Reflect.lookupInstantiatableClass(fqcn)
  .getOrElse(throw new ClassNotFoundException(fqcn))
  .runtimeClass

Can you just use ClassTag[A].newArray?

Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez

2025-07-02 14:57:42 +00:00
Commented Jul 2 at 14:57 — Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez, Commented Jul 2 at 14:57

Gaël J · Accepted Answer · 2025-07-02 16:36:56Z

3

You cannot get a java.lang.Class from a string. There's the reflection API, as you noticed, but that is only for very specific classes that have been annotated with @EnableReflectiveInstantiation. This is usually only used by test framework classes.

The Scala way would be to take an implicit ClassTag[A], which is the defining purpose of ClassTag. An alternative is to pass the java.lang.Class as argument, and at call site, give it as a classOf[C] for a concrete C.

From a string, it's not possible.

edited Jul 2 at 16:36

Gaël J

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answered Jul 2 at 15:03

sjrd

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