`// Where script returns a 'function () {}' object.
final String script = someScript;
// ScriptUtils comes from jdk.nashorn.api.scripting.ScriptUtils
final ScriptObjectMirror som = ScriptUtils.unwrap(engine.eval(source ));
/* This object will be created once and kept around to avoid re-creating
 it through ScriptObjectMirror#call varargs. */
Object[] args = something;
// Then calling the js function object with itself as 'this'.
som.call( som, args );`

`// 'context' is a Java object.
function (context) {
  let id = context.ownerId;
  let data = context.dataFor(id);
  // do things with data and context.
}`