Workshop › Scorched Earth-style Artillery › Step 6 of 23

Aim

What we are doing

Left and right turn your barrel, up and down change the power. The angle stays between flat left and flat right, and the power between 2 and 12.

```js
const MAX_POWER = 12

function aimBy(dAngle, dPower) {
  const t = tanks[0]
  t.angle = Math.max(-Math.PI, Math.min(0, t.angle + dAngle))
  t.power = Math.max(2, Math.min(MAX_POWER, t.power + dPower))
}

document.addEventListener('keydown', (event) => {
  if (event.key === 'ArrowLeft') aimBy(-0.03, 0)
  else if (event.key === 'ArrowRight') aimBy(0.03, 0)
  else if (event.key === 'ArrowUp') aimBy(0, 0.25)
  else if (event.key === 'ArrowDown') aimBy(0, -0.25)
  else return
  event.preventDefault()
})
```

What it means

aimBy changes the angle and power by the given amounts, then keeps them within their limits.
The angle -Math.PI is flat left, 0 flat right; everything between points up.
else return leaves other keys alone; only the arrow keys are kept from scrolling the page.

Your turn

Under H, write MAX_POWER.
Above draw, write aimBy and the key listener.

Skills: Keyboard and mouse input

← The game loop Angle and power →

All steps