Workshop › Zelda-style Dungeon › Step 16 of 22

A world that remembers

What we are doing

Leave the room and come back: the heart is there again, because enter loads the room fresh. The world must remember what was taken. Every taken tile gets a name like '0,0,11,7' (room and tile), kept in a Set; enter turns those tiles into floor.

```js
let taken // what has been picked up or opened in each room, so it stays that way

  taken = new Set()

// Load a room: its tiles (minus what was already taken), and fresh enemies on its e tiles.
function enter(rx, ry) {
  room = { rx, ry }
  tiles = ROOMS[ry][rx].map((line, row) =>
    [...line].map((ch, col) => (taken.has(rx + ',' + ry + ',' + col + ',' + row) ? '.' : ch === 'P' || ch === 'e' ? '.' : ch)),
  )

  const id = room.rx + ',' + room.ry + ',' + col + ',' + row

    taken.add(id)
```

What it means

• A Set is a collection without repeats; has asks if a name is in it, add puts one in.
• The name joins the room's and the tile's numbers with commas, so every tile in the world has its own name.
• enter now needs row and col too, to build each tile's name.

Your turn

1. Under tiles, write taken; at the top of reset, make it a new Set.
2. Rewrite the tiles line of enter to skip taken tiles, and write the comment above enter.
3. In update, name the tile under the hero, and remember it when something is picked up.

Skills: Game states, Arrays and objects

← Keys and hearts The locked door →

All steps

1. A room
2. The hero
3. The game loop
4. Walk
5. Walls
6. A touch pad
7. Next room
8. The sword
9. Enemies
10. Strike!
11. They chase you
12. They wander
13. Ouch
14. Blinking and hearts
15. Keys and hearts
16. A world that remembers
17. The locked door
18. A timer
19. Game over
20. The stairs out
21. Best time
22. Build it yourself: cleared rooms