How to load java script having class, in jvm using nashorn

Here is my simple java script test.js with class :

class Car {
  constructor(name, year) {
    this.name = name;
    this.year = year;
  }
}

myCar = new Car("Ford", 2014);

Print("done")

Here is my java code which will try to load test.js

public class Controller {

    public static void main(String[] args) {

        try {
        
        NashornScriptEngineFactory factory = new NashornScriptEngineFactory();
        ScriptEngine engine = factory.getScriptEngine("--language=es6");

        engine.eval(Files.newBufferedReader(Paths.get("<Path-to-test-js>/test.js"), StandardCharsets.UTF_8));
        } catch (Exception _e){
            System.out.println(_e);
        }
    }

but its throwing exception :

javax.script.ScriptException: <eval>:1:0 Expected an operand but found class
class Car {
^ in <eval> at line number 1 at column number 0

Why its throwing exception here.