Workshop › Klondike Solitaire › Step 6 of 40

Shuffle

What we are doing

A new deck is in order. We shuffle it the fair way: going from the last card to the first, swap each card with a random card at or before it.

```js
for (let i = deck.length - 1; i > 0; i--) {
  const j = Math.floor(Math.random() * (i + 1))
  ;[deck[i], deck[j]] = [deck[j], deck[i]]
}
```

What it means

• The loop counts i down from 51 to 1 (i-- takes 1 off).
• Math.random() * (i + 1) is a number from 0 to just under i + 1; Math.floor cuts the decimals: a whole number from 0 to i.
• [deck[i], deck[j]] = [deck[j], deck[i]] swaps two cards in one line. The ; in front stops JavaScript from gluing this line (it starts with [) onto the line before.

Your turn

In newDeck, between the for line that builds the deck and return deck, write the shuffle loop.

Skills: Arrays and objects, Loops

← A deck of 52 Piles in one object →

All steps

1. The green table
2. Draw one card
3. The face of a card
4. Red and black
5. A deck of 52
6. Shuffle
7. Piles in one object
8. Deal the seven columns
9. A place for every pile
10. Put the piles on the table
11. Fan out the columns
12. Outlines for empty places
13. Turn over a card
14. Space turns a card
15. Go through the stock again
16. What is under the pointer?
17. Hitting a card in a column
18. Tap the stock
19. Rule 1: building a column
20. Rule 2: building a foundation
21. Move cards by the rules
22. Turn over the uncovered card
23. Find where a card goes
24. Pick up a card
25. Tap to move
26. A move counter
27. Count the moves
28. Where did you grab it?
29. Follow the pointer
30. Draw the held cards at the pointer
31. Drop it where you want
32. Drop a king into an empty column
33. A clock
34. Winning
35. You won!
36. A new game
37. The best time
38. Snapshots of the table
39. Undo
40. Build it yourself: finish by itself