Built a standalone browser Gomoku game in , , and . It renders a 15x15 board, lets the player place black stones, detects wins in all four directions, highlights the winning line, tracks turns and move count, and supports restarting the match.
The AI is heuristic rather than random. It searches nearby candidate moves, scores offensive patterns for itself, scores defensive blocks against the player, adds center preference, and chooses the strongest move. There's also an optional “AI focus area” overlay so you can see the strongest candidate points it considered.
Verification: node --check app.js passed. I did not run an interactive browser session here, so the remaining step is to open in a browser and play.