Workshop › Doodle Jump-style Climber › Step 21 of 24

Moving platforms

What we are doing

Higher up, some platforms slide from side to side (blue). The chance grows with the difficulty, up to one in two.

```js
const COLORS = { normal: '#16a34a', moving: '#2563eb' }

    if (Math.random() < d * 0.5) {
      platform.kind = 'moving'
      platform.vx = 1.5
    }

  for (const p of platforms) {
    p.x += p.vx
    if (p.x < 0 || p.x + p.w > canvas.width) p.vx = -p.vx
  }
```

What it means

• Math.random() < d * 0.5 is never true at difficulty 0 and true half the time at 1.
• Every frame each platform moves by its vx; at an edge the speed flips sign, so it comes back.

Your turn

1. Add moving: '#2563eb' to COLORS.
2. In fillPlatforms, before platforms.push(platform), write the chance block.
3. In update, after the wrap lines, write the loop that moves the platforms.

Skills: Game states, Velocity and gravity

← Kinds of platform Traps →

All steps

1. The jumper
2. Draw again and again
3. Gravity
4. Bounce
5. Steer left and right
6. Through the sides
7. Half here, half there
8. Touch steering
9. Platforms
10. Land on platforms
11. A camera that follows
12. Lines on the wall
13. How hard should it be?
14. Endless platforms
15. Miss and fall
16. Play again
17. Tap to play again
18. Score is height
19. Best score
20. Kinds of platform
21. Moving platforms
22. Traps
23. It breaks!
24. Build it yourself: springs