Workshop › Bomberman-style Arena › Step 34 of 42

Hidden power-ups

What we are doing

About one crate in five hides a power-up: 'bomb' (one more bomb at a time) or 'fire' (longer flames). They are kept in a Map from a tile to its item; only tiles that have something take space.

```js
let items // 'r,c' -> 'bomb' or 'fire', hidden under crates until they burn

const key = (r, c) => r + ',' + c

  items = new Map()

      else {
        grid[r].push('+')
        if (Math.random() < 0.2) items.set(key(r, c), Math.random() < 0.5 ? 'bomb' : 'fire')
      }
```

What it means

• A Map stores values under keys: set(key, value), get(key), has(key), delete(key).
• Keys must be simple values to be found again, so a tile becomes a string: key(3, 5) is '3,5'.
• The crate branch now does two things, so it gets { }: place the crate, then a 20% chance to hide an item, half bombs and half fire.

Your turn

1. Under let grid write let items; above near write key.
2. In makeGrid, under grid = [], write items = new Map().
3. Replace else grid[r].push('+') with the else { ... } block.

Skills: Arrays and objects, Game states

← All enemies gone Uncover the power-ups →

All steps

1. Measure the arena
2. A floor of tiles
3. Draw it every frame
4. The arena as data
5. Draw what the grid says
6. Pillars
7. Crates
8. Keep the corners clear
9. The player
10. Keys being held
11. Slide towards a target
12. Walk
13. Drop a bomb
14. Space drops, bombs show
15. One bomb at a time
16. Bombs are in the way
17. The fuse burns down
18. Fire!
19. Flames die down
20. A cross of flames
21. Crates burn
22. Chain reactions
23. Bombs blink
24. Flames hurt
25. A moment of safety
26. Hearts
27. Out of lives
28. Game over
29. Enemies
30. Enemies wander
31. No turning back
32. Fight and touch
33. All enemies gone
34. Hidden power-ups
35. Uncover the power-ups
36. Pick them up
37. Show the powers
38. Which way is the finger?
39. Play with a finger
40. A clock
41. The fastest win
42. Build it yourself: a smarter enemy