Workshop › Chess › Step 46 of 48

The computer plays black

What we are doing

Connect the computer to the game. After a move that gives black the turn, thinking = 20: the game waits 20 frames (a third of a second) so you see your move land. update counts down on black's turn and then plays computerMove(). The loop calls update before drawing.

```js
let thinking // frames until the computer moves

  thinking = 0

  if (legalMoves().length === 0) state = inCheck(turn) ? 'checkmate' : 'stalemate'
  else if (turn === 'b') thinking = 20

function update() {
  if (state !== 'playing' || turn !== 'b') return
  thinking -= 1
  if (thinking <= 0) play(computerMove())
}

function loop() {
  update()
  draw()
```

What it means

• else if runs only when the game is not over: then, if black is to move, start the wait.
• update does nothing unless the game is on and it is black's turn; each frame thinking goes down by 1, and at 0 the computer's move is played with the same play your clicks use.

Your turn

1. Under let state ... write let thinking ...; in reset, under state = 'playing' write thinking = 0.
2. In play, under the if (legalMoves()... line write the else if line.
3. Above function draw() { write update.
4. In loop, above draw() write update().

Skills: The game loop, Game states

← Try the best-looking moves first You are white →

All steps

1. A dark table
2. One row of squares
3. All 64 squares
4. The starting position as text
5. Color and kind
6. Draw the pieces
7. An outline for white
8. Draw again and again
9. The knight's jumps as data
10. A list of moves
11. The king steps too
12. Which square was clicked?
13. Light up the selected square
14. Whose turn is it?
15. Where can it go?
16. Show the targets
17. Play a move
18. Click a dot to move
19. Say whose turn it is
20. The rook slides
21. Bishops and queens
22. Pawns step forward
23. Pawns capture diagonally
24. A pawn becomes a queen
25. Is a square attacked?
26. Attacks from far away
27. Is the king in check?
28. A move that remembers
29. Take a move back
30. Only legal moves
31. Castling moves
32. The rook jumps over
33. Losing the right to castle
34. No castling through check
35. Remember the double step
36. En passant
37. Checkmate and stalemate
38. Check! and the result
39. Click to play again
40. Show the last move
41. A score for a position
42. Thinking ahead
43. Pick the best move
44. Alpha-beta: skip what cannot matter
45. Try the best-looking moves first
46. The computer plays black
47. You are white
48. Build it yourself: the fifty-move rule