tictactoe: try it here!
A Tic Tac Toe game I created to learn JS, HTML and CSS. The board size and win requirements can be specified by the user so you can also play 5-in-a-row (gomoku) or whatever weird game you want. The main challenges were making the UI responsive to screen size, decoupling HTML, CSS and JavaScript as much as possible and controlling form input by the user to disallow nonsensical states.