Help with Tic-Tac-Toe?

I have no idea how to make the alert pop up that anyone has won, nor have I figured out how the computer to make its move. I know it’s definitely not my best code, but I figured I can clean it up later once I understand the logic.

Have you looked at the browser’s console (Ctrl+Shft+J in Chrome) to see if you have any errors showing?

Quite honestly, I don’t even know how to do that. Using safari, too.

To access the developer console in Safari, use the Develop > Show Error Console menu item (Option-Cmd-C):