Workshop › Space Invaders-style › Step 20 of 21

Faster and faster

What we are doing

The fewer invaders are left, the faster they march — the famous tension of the game. Later waves are quicker too.

```js
// Fewer invaders march faster: from 588 ms with all 45 alive down to 60 ms for the last one, quicker in later waves.
function stepInterval() {
  return Math.max(40, 60 + (alive().length - 1) * 12 - (wave - 1) * 40)
}
```

What it means

• Each living invader beyond the last adds 12 ms; each wave after the first takes 40 ms off.
• Math.max(40, ...) never lets the step be quicker than 40 ms.

Your turn

Replace the body of stepInterval with the formula, and write the comment above it.

Skills: Game states, Functions

← Waves Build it yourself: an extra life →

All steps

1. The ship
2. The game loop
3. Move the ship
4. Stay on screen
5. Fire
6. Bullets fly
7. A short reload
8. The invaders
9. The march
10. Hit!
11. Score
12. They shoot back
13. Bombs fall
14. Lives
15. Game over
16. Best score
17. A wave in a function
18. Play again
19. Waves
20. Faster and faster
21. Build it yourself: an extra life