The undefined
is the return value of console.log(...)
.
You can see this by defining two functions in the console, one returning something, and the other returning nothing, e.g. like this:
function f1() {
return 1;
}
function f2() {
return;
}
And then calling them separately (manually)
f1(); // shows '1'
and
f2(); // shows 'undefined'
Also note the little symbol before these return value string.