Is using custom functions a preference? It's possible to make a game work with everything happening inside event listeners but I want to know how often should I use functions. Like in a game of Tic Tac Toe, if I click on a square it will change color, the turn variable will change, check if there are any winners or anymore moves. For all that I just put all the results in that Mouse_CLICK event listener. I don't know when I should use custom functions.