Why is my code logging undefined at the end?

I was working on a JavaScript challenge - Chess Board- from Eloquent JavaScript (http://eloquentjavascript.net/02_program_structure.html) and came up with my own solution that works, but it logs undefined at the end. And I'd like to know- Why?

Here is a link to my codepen. It's not very pretty bc I take notes as I work through the code. https://codepen.io/maribies/pen/WZyqXE

Here is the code I wrote as well-

var size = 8;

var symbol = function(size*1/2) { var result = ""; for (var count = 0; count < size; count++) result += "# "; return result; } var space = function(size*1/2) { var result = ""; for (var count = 0; count < size; count++) result += " #"; return result; }

function chessBoard() { var result = ""; for (var count = 0; count < (size*1/2); count++) result += console.log( symbol(size)), console.log(space(size)); };

console.log(chessBoard());

I understand that it might not be the 'best' solution, but I do want to understand why it also returns undefined at the end.

Thanks.

(Also, if it's worth it, is there a was to refactor this code to condense the # of lines? Thanks!)