gistfile1.txt

<script src="acorn.js"></script>
<script src="interpreter.js"></script>
<script>
var externalObject = {x:100}
var modifiedObject = {x:100}

var modFunction = function(data) {
  modifiedObject.x = data;
}

var code = "alert(internalObject.x);internalObject.setExternalObject(2000);"

var interpreter = new Interpreter(code, function(interpreter, scope) {
  var myObject = this.createObject(interpreter.OBJECT);
  this.setProperty(scope, 'internalObject', myObject);
  this.setProperty(myObject,'x',this.createPrimitive(externalObject.x))
  this.setProperty(myObject, 'setExternalObject', this.createNativeFunction(function(data) {
        return interpreter.createPrimitive(modFunction(data));
      })
    )

  var wrapper = function(text) {
    text = text ? text.toString() : '';
    return interpreter.createPrimitive(alert(text));
  };
  interpreter.setProperty(scope, 'alert',
      interpreter.createNativeFunction(wrapper));
})

interpreter.run()
alert(modifiedObject.x)
</script>