When to use internal function and when not to?

Question

I am using more and more javascript in my work and wonders what is good practice when it comes to the examples below.

function foo(){
    //do stuf
    var bar = foo2();
    //do stuf

    function foo2(){
        //do stuf
        return aValue;
    }
}

No other functions needs to know about foo2() which is why I sometimes hides it in foo(). The downside is that I think that readability of foo() is lost and it could be harder to locate foo2(). Is this good practice or should I rather do it like this:

function foo(){
    //do stuf
    var bar = foo2();
    //do stuf
}
function foo2(){
    //do stuf
    return aValue;
}