Workshop › Lunar Lander › Step 10 of 31

Around the sides

What we are doing

A lander that leaves one side of the screen comes back on the other. The remainder operator % does it in one line.

```js
// Leaving one side brings the lander back on the other.
lander.x = (lander.x + canvas.width) % canvas.width
```

What it means

• % gives the remainder: 490 % 480 is 10.
• Adding 480 first keeps negative positions working: (-3 + 480) % 480 is 477.

Your turn

In update, under lander.y += lander.vy, write the comment and the new line.

Skills: Velocity and gravity

← Moon gravity Flying or not →

All steps

1. Random hills
2. Draw the hills
3. A landing pad
4. The height at any x
5. The lander
6. Draw it around its own middle
7. Two feet
8. The game loop
9. Moon gravity
10. Around the sides
11. Flying or not
12. Touching the ground
13. Remember held keys
14. Tilt
15. The engine
16. A flickering flame
17. Fuel
18. Touch controls
19. Landing or crashing
20. Fly again
21. Landed or crashed?
22. Readouts
23. Levels
24. Score
25. Next level or new game
26. A narrower pad
27. A high score
28. Burst into pieces
29. Pieces fall and fade
30. Draw the wreck
31. Build it yourself: wind