Workshop › Memory › Step 15 of 25

One place for the rules

What we are doing

Turning a card over is about to get rules: pairs, a limit of two cards, moves. We give it its own function, flip, and the click only calls it. It refuses a missing card or one that is already face up.

```js
function flip(card) {
  if (!card || card.faceUp) return
  card.faceUp = true
}

  flip(cardAt(x, y))
```

What it means

• !card means "there is no card". || means "or".
• return leaves the function at once, so the card is only turned when both checks pass.
• The click now just calls flip(cardAt(x, y)).

Your turn

1. Above the click listener, write flip and an empty line.
2. In the listener, replace the last two lines with flip(cardAt(x, y)).

Skills: Functions

← Click to turn a card Two cards at a time →

All steps

1. Get the canvas and the pen
2. The table
3. One card
4. A row of cards
5. Four rows
6. Every fruit twice
7. Cards that know themselves
8. A card's corner
9. Draw the cards from the list
10. Draw again and again
11. The face of a card
12. A fair shuffle
13. Which card is at a point?
14. Click to turn a card
15. One place for the rules
16. Two cards at a time
17. Pair or no pair
18. Count the moves
19. Show moves and pairs
20. All pairs found
21. Play again
22. A number that follows
23. Swap sides halfway
24. Animate the turn
25. Build it yourself: your best game