Workshop › Mario-style Platformer › Step 14 of 37

Jump

What we are doing

A jump is just an upward speed: vy = JUMP, a negative number. Gravity does the rest: it slows the rise, turns it into a fall and lands the player. You may only jump while standing on something.

```js
const JUMP = -11.5

function jump() {
  if (player.grounded) {
    player.vy = JUMP
  }
}

  if ((event.key === ' ' || event.key === 'ArrowUp') && !event.repeat) jump()
```

What it means

• JUMP is negative because up is negative y.
• jump only works when grounded.
• Space or the up arrow call it. event.repeat is true for the automatic repeats of a held key, so holding the key does not jump again and again.

Your turn

1. Under FRICTION write JUMP.
2. Above the keydown listener write jump, with an empty line after it.
3. In the keydown listener, under keys[event.key] = true, write the jump line.

Skills: Keyboard and mouse input, Velocity and gravity

← Walls Bump your head →

All steps

1. The sky
2. A level made of text
3. Draw the tiles
4. What is solid?
5. Is a box touching anything?
6. Find the start
7. Draw the player
8. Gravity
9. Landing on tiles
10. Which keys are held?
11. Speed up
12. Friction
13. Walls
14. Jump
15. Bump your head
16. Short hops
17. A few frames of grace
18. Coyote time
19. A camera that follows
20. Stop at the ends
21. Draw only what is on screen
22. Coins
23. Collect them
24. Count, and screen versus world
25. Enemies
26. Enemies that walk
27. Do not walk off ledges
28. Lives and a fresh start
29. Falling into a pit
30. Enemies hurt
31. Stomp!
32. Squashed enemies are gone
33. Game over
34. Play again
35. The flag
36. Reach the flag
37. Build it yourself: jump buffering