Looks like this is pretty much identical to JavaScript?

Pretty much. Javascript has the same scoping rules for functions used as expressions:

    var f = function fac(n) { if (n==0) { return 1; } else {return fac(n-1)*n; } };
    console.log(f(3));
    console.log(fac(3));

This will log '6' and error out on the last one (fac is undefined). This is the same scoping Erlang uses for anonymous function names as far as I can tell, with one difference: Erlang's function name is a variable that can be used as such internally. In Javascript, the function name doesn't refer to a variable per se:

    var f = function fac() { console.log(fac) };
    console.log(f);
    f();

Which will log 'fac()' and 'undefined'. In Erlang:

    1> F = fun Fac() -> Fac end.
    #Fun<erl_eval.44.71889879>
    2> F().
    #Fun<erl_eval.44.71889879>
 

Both instances (F and Fac within the right scope) return the same anonymous function.

Are you sure you didn't make a mistake, and confuse the undefined that f() returned with an undefined output from the console.log(fac)? It looks to me like the function is a perfectly normal variable.

    var f = function foo() { console.log('Me:', foo); }
    f();
    Me: function foo() { console.log('Me:', foo); }
    undefined

You're right, I've been fooled by Firebug merging in multiple identical output lines together and missed the (2) it had put on the right hand side of the screen. That makes a lot more sense.