How to run JavaScript code from within Scala (JVM)?

Question

Is there any library that allows us to run a JavaScript code (as a String) from Scala code? Whether the JavaScript code is running in the JVM or a spawned JavaScript interpreter is not important.

Answer 1

If you want to use the current JVM process, use JVM's ScriptEngine.

import javax.script.ScriptEngineManager

val engine = new ScriptEngineManager().getEngineByMimeType("text/javascript")
val result = engine.eval("1 + 1")
println(result)

This uses Rhino for JDK 7 and Nashorn for JDK 8.

The interaction between Java code and Nashorn is rather seamless.

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If you want to use a new process, use ProcessBuilder with an external JS runtime.

import java.io.ByteArrayInputStream
import scala.sys.process._

val input =  new ByteArrayInputStream("console.log(1 + 1)".getBytes)
val result = ("node" #< input).!!
println(result)

This will give you perhaps the fastest execution if the JS is heavy on CPU usage. It also allows the JS to use the Node.js APIs, though it requires Node.js to be installed.

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If you want to use the current JS process (i.e. if you are using Scala.js),

import scala.scalajs.js

val result = js.eval("1 + 1")
println(result)

Answer 2

Try to use Rhino or Nashorn it's on Java, but you can use it from Scala