Workshop › Connect Four › Step 7 of 38

The board in memory

What we are doing

The game must remember what is in every hole. The board becomes a 2D array: a list of 6 rows, each a list of 7 cells. board[row][col] is 0 for empty, 1 for red and 2 for yellow. Every row must be its own new array.

```js
let board // board[row][col]: 0 empty, 1 or 2

function reset() {
  board = Array.from({ length: ROWS }, () => Array(COLS).fill(0))
}

reset()
```

What it means

• Array(COLS).fill(0) is a row of seven 0s.
• Array.from({ length: ROWS }, () => ...) calls the arrow function once per row, so each row is a new array.
• The classic bug Array(ROWS).fill(Array(COLS).fill(0)) would put the same row six times: change one, change all.

Your turn

1. Under the constants, after an empty line, write let board and reset.
2. Above the draw() call at the bottom, write reset().

Skills: Arrays and objects

← All 42 holes Discs in their colors →

All steps

1. A dark background
2. A drawing function
3. The blue board
4. One hole
5. A whole row
6. All 42 holes
7. The board in memory
8. Discs in their colors
9. Draw every frame
10. Where does the disc land?
11. Play a column
12. Taking turns
13. Click to play
14. The next disc
15. Whose turn?
16. Playing with the keyboard
17. Keys 1 to 7
18. A disc on its way
19. Gravity
20. Watch it fall
21. Inside the board?
22. Walking along a line
23. Four in a row?
24. We have a winner
25. Circle the four
26. Who won?
27. A draw
28. Play again
29. Try a move and take it back
30. Win, or block
31. Don't help the player
32. Prefer the middle
33. The computer's turn
34. Only on your turn
35. You and the computer
36. Counting wins
37. Show the score
38. Build it yourself: the loser starts