Workshop › Connect Four › Step 21 of 38

Inside the board?

What we are doing

To find four in a row we will walk from cell to cell. We must never step off the board, so first a small helper: inside(row, col) is true only for a cell that exists.

```js
const inside = (row, col) => row >= 0 && row < ROWS && col >= 0 && col < COLS
```

What it means

• An arrow function kept in a constant. With no { } after =>, the value on the right is returned.
• && needs all four checks to be true: the row from 0 to 5 and the column from 0 to 6.

Your turn

Above function play( write inside, followed by an empty line.

Skills: Functions

← Watch it fall Walking along a line →

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