ADDITIONAL SYSTEM INFORMATION :
<dependency>
            <groupId>org.openjdk.nashorn</groupId>
            <artifactId>nashorn-core</artifactId>
            <version>15.4</version>
        </dependency>

A DESCRIPTION OF THE PROBLEM :
scriptObject should not be array, but it is now array

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
a
b
c
ACTUAL -
0,a
1,b
2,c

---------- BEGIN SOURCE ----------
public class Main {
    public static void main(String[] args) throws ScriptException {
        ScriptEngine engine1 = new NashornScriptEngineFactory().getScriptEngine(new String[]{"--language=es6"});
        Object arr = engine1.eval("['a', 'b', 'c']");

        System.out.println("bug?");
        ScriptEngine engine2 = new NashornScriptEngineFactory().getScriptEngine(new String[]{"--language=es6"});
        engine2.put("arr", arr);
        engine2.eval("for (var a of arr) {\n" +
                "\tprint(a)\n" +
                "}");
    }
}
---------- END SOURCE ----------

FREQUENCY : always