Weird output of [97,98].map(String.fromCharCode)

Question

this works as expected

[97,98].map(function(x){String.fromCharCode(x)})
// [ \'a\', \'b\' ]

but the output is following line is unexpected<

Answer 1

       a2 = [97,98].map(function(x){return String.fromCharCode(x)});
       alert(a2);
       a2 = [97,98].map(String.fromCharCode);
       alert(a2);

both alert "a,b" for Firefox13 on Linux. the first function was missing a return statement.