Workshop › Missile Command-style Defense › Step 4 of 35

Cities that can fall

What we are doing

A city can be destroyed, so each city needs to remember whether it is still standing. reset() turns the list of x positions into a list of city objects.

```js
let cities

function reset() {
  cities = CITY_XS.map((x) => ({ x, alive: true }))
}

reset()
```

What it means

• map makes a new list by passing every item through a function: each x becomes { x, alive: true }.
• { x } is shorthand for { x: x }. The extra ( ) around the object are needed, or { would start a function body.
• reset() is called once, before the loop starts.

Your turn

1. Under const CITY_XS = ... leave an empty line and write let cities and the reset function.
2. Write reset() just above the last requestAnimationFrame(loop).

Skills: Arrays and objects, Game states

← Draw again and again Rubble →

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