windows node.js REPL command prompt error messages

I am complete new to open source and would really like to use it more. I installed (x86)node.js from nodejs.org. I launched "Node.js command prompt" from the installed list, and executed node.exe. I am trying to to run some sample javascript. Why is it if I do:

>var life = 11;
undefined
^^^^^^^^^
why am I getting this message?

or 

>a = [1,2,3]
[1,2,3]
>a.forEach(function (v) {console.log(v);});
1
2
3
undefined 
^^^^^^^^^
//still get this, even though the script executed??
>

undefined is just the return value of the statements you executed. Only meaningful/useful if you've executed a function, really.

The console prints the return value of your script, which is undefined

Write this:

"hello";

And press enter. Now the return value should be "hello" and not undefined.

You could also do;

var life = 11; life;