Scripting using JavaScript: How to print value?

I know how to get the value of particular XML element by using getNodeValue() method but I am not able to print this value. How can I do this with JavaScript. I am also not able to use log.info statement. Can somebody help me with this.

Also, I didn't find any tutorial which explains script assertions using JavaScript language. It would be very helpful if you pass any good link.
Thanks.