Workshop › Missile Command-style Defense › Step 31 of 35

Launch from anywhere

What we are doing

Soon some missiles will split in the air. The pieces must start where the missile is, not at the top. So launch gets a starting point, with the top edge as the default.

```js
function launch(sx = Math.random() * canvas.width, sy = 0) {

  incoming.push({ sx, sy, x: sx, y: sy, tx, ty: GROUND, speed: 0.5 + wave * 0.15 })
```

What it means

• sx = ... and sy = 0 are default parameters: used only when launch is called without them.
• launch() still makes a normal missile at the top; launch(100, 150) starts one at (100, 150).
• The old const sx line is no longer needed.

Your turn

1. Change the launch line as shown and delete the const sx = ... line under it.
2. In the push line, use sy instead of sy: 0, and y: sy instead of y: 0.

Skills: Functions

← Wave, ammo and messages Some missiles will split →

All steps

1. Six cities to protect
2. Your missile base
3. Draw again and again
4. Cities that can fall
5. Rubble
6. Move towards a point
7. Launch an enemy missile
8. One missile a second
9. Missiles on their way
10. Smoke trails
11. Impact
12. Fire an interceptor
13. Click the sky
14. Interceptors fly
15. An explosion that grows and shrinks
16. Explode on arrival
17. Draw the explosions
18. Impacts explode too
19. Caught in the blast
20. Chain reactions
21. Only your explosions count
22. Points for every missile
23. Show the score
24. Limited ammo
25. Waves
26. Each wave is harder
27. The end of a wave
28. The end
29. Play again
30. Wave, ammo and messages
31. Launch from anywhere
32. Some missiles will split
33. Split into three
34. A high score
35. Build it yourself: a crosshair