ChanceJS from Groovy / Java

Chance.groovy

package vendigo.support.extensions

import groovy.json.JsonOutput

import javax.script.ScriptEngine
import javax.script.ScriptEngineManager

class Chance {

  private static ScriptEngine engine

  static {
    ScriptEngineManager factory = new ScriptEngineManager()
    engine = factory.getEngineByName("nashorn")
    engine.eval("""
      var window = { document: {} }

      var JavaMath = Java.type('java.lang.Math')
      load('./node_modules/chance/dist/chance.min.js')
      window.chance.random = JavaMath.random
    """)
  }

  def methodMissing(String name, args) {
    String options = args ? JsonOutput.toJson(args[0]) : ''
    return engine.eval("window.chance.${name}(${options})")
  }

}

You can now get the full feature set of ChanceJS in Groovy thanks to the joys of Metaprogramming!

For Java you will have to adapt this to define the methods you want to use.

To use:

Chance chance = new Chance()
println chance.word() // prints 'woswoswos' or similar
println chance.phone( country: 'uk', formatted: false ) // prints '01614329918' or similar

This is awesome!

Just curious, how does it deal with the dynamically-typed/statically-typed barrier from JavaScript to Groovy? Does it do type inference based on what is returned from Chance or does it just assume all responses are strings and leave it to an exercise to the user to cast them as the appropriate type or something else? (sorry I know nothing about Groovy)

@victorquinn I'm not 100% sure as I'm very new to the Nashorn engine, but it seems to do the same coercion as the JsonSlurper / JSONObject classes do, so it returns the equivalent groovy/java objects, which works for every case other than large numbers (which end up as things like 6.99999999999E11. What I've done in the case of numbers is taken the Groovy approach of wrapping them with BigDecimal which makes the representation sane again.

Everything else (so far) appears to be "Automagic"

So I found that there was no randomness at all, for some reason chance.random() doesn't generate random numbers at all.

So I've overriden chance's random number generator to use Java's builtin random number generator.

I've gone deep now, way too meta, but it works flawlessly 👯

engine.eval("""
  var window = { document: {} }
      var JavaMath = Java.type('java.lang.Math')
      ${chanceJs}
      window.chance.random = JMath.random
""")