Workshop › Space Invaders-style › Step 17 of 21

A wave in a function

What we are doing

When all invaders are gone, a new wave should come. So building the formation moves into a function, spawnWave, which also clears the bullets and bombs and starts the march fresh. The game calls it once at the start.

```js
let bullets
let invaders
let bombs
let dir // +1 marching right, -1 marching left
let lastStep
let lastShot = -COOLDOWN

function spawnWave() {
  invaders = []
  for (let row = 0; row < ROWS; row++) {
    for (let col = 0; col < COLS; col++) {
      invaders.push({ x: 40 + col * SPACING_X, y: 60 + row * SPACING_Y, w: INVADER_W, h: INVADER_H, row, alive: true })
    }
  }
  bullets = []
  bombs = []
  dir = 1
  lastStep = now
}

spawnWave()
```

What it means

The variables are only declared at the top; spawnWave gives them their values.
lastStep = now makes the first march step come half a second after the wave appears.

Your turn

Replace the variables from bullets to lastStep with the short list.
Above overlaps, write spawnWave.
At the bottom, call spawnWave() above requestAnimationFrame(loop).

Skills: Functions

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