Workshop › Sokoban › Step 23 of 29

A photo of the game

What we are doing

One careless push can make a level impossible, so we will add undo. First, snapshot() turns everything a move can change into one piece of text: a photo of the game. history will keep the photos.

```js
let history

  history = []

function snapshot() {
  return JSON.stringify({ player, boxes, moves })
}
```

What it means

• history is the list of photos, emptied on every load.
• { player, boxes, moves } is an object with the three things a move can change.
• JSON.stringify turns it into text: a real copy. Storing the boxes array itself would store the same array, and the next push would change the "saved" copy too.

Your turn

1. Under let moves write let history.
2. At the end of loadLevel, under moves = 0, write history = [].
3. Above function move, write snapshot. Press Run.

Skills: Game states

← Count the moves A photo before every move →

All steps

1. A level written as text
2. The canvas and the pen
3. The warehouse floor
4. A function that draws
5. A name for every tile
6. Read the walls
7. Draw the walls
8. Center the level
9. The goals
10. The boxes
11. The player
12. Two more levels
13. One step
14. Walk with the arrows
15. Boxes are in the way
16. Push a box
17. A box on a goal turns green
18. Solved!
19. On to the next level
20. Which level?
21. A line at the bottom
22. Count the moves
23. A photo of the game
24. A photo before every move
25. Undo
26. Restart
27. A record for every level
28. Show the record
29. Build it yourself: count the pushes