Karate API test gives javascript evaluation failed error when reading karate-config.js

Question

I just started using karate and want to use karate-config.js to config it. In Maven, I have

    <dependency>
        <groupId>com.intuit.karate</groupId>
        <artifactId>karate-core</artifactId>
        <version>0.6.0</version>
    </dependency>

    <dependency>
        <groupId>com.intuit.karate</groupId>
        <artifactId>karate-apache</artifactId>
        <version>0.6.0</version>
    </dependency>

    <dependency>
        <groupId>com.intuit.karate</groupId>
        <artifactId>karate-junit4</artifactId>
        <version>0.6.0</version>
    </dependency>

and I put karate-config.js under resource folder:

function() {
    var env = karate.env; // get java system property 'karate.env'

    karate.log('karate.env selected environment was:', env);
    karate.configure("ssl", true)

    if (!env) {
    env = 'dev'; //env can be anything: dev, qa, staging, etc.
    }

    var config = {
    env: env,

    AM_USERNAME: 'devuser',
    AM_PASSWORD: 'devpass',
    AM_HOST: 'https://am.'+env+'.example.net',
    AM_AUTHENTICATE_PATH: '/am/json/realms/root/authenticate',

...

starter.java

@RunWith(Karate.class)
@CucumberOptions(features = "classpath:karate")
public class StartCucumberApiTest {
}

But when I try to run, I got this:

java.lang.RuntimeException: bootstrap configuration error, evaluation of karate-config.js failed: Caused by: java.lang.RuntimeException: javascript evaluation failed: function() { var env = karate.env; // get java system property 'karate.env'

Seemed java can not evaluate karate-config.js

1. Why it is javascript for config?
2. Obviously, java can not parse this javascript config file, so how can I put and make karate-config.js working?

Thanks