Workshop › Asteroids › Step 12 of 41

Making a bullet

What we are doing

Many bullets can fly at once, so they go in an array. shoot adds one at the ship's nose. Its velocity is the direction times BULLET_SPEED, plus the ship's own velocity, like a ball thrown from a moving car.

```js
const BULLET_SPEED = 7
const BULLET_LIFE = 55 // frames

let bullets

function shoot() {
  const dx = Math.cos(ship.angle)
  const dy = Math.sin(ship.angle)
  bullets.push({
    x: ship.x + dx * SHIP_R,
    y: ship.y + dy * SHIP_R,
    vx: ship.vx + dx * BULLET_SPEED,
    vy: ship.vy + dy * BULLET_SPEED,
    life: BULLET_LIFE,
  })
}

bullets = []
```

What it means

dx, dy are the direction the ship faces, worked out once.
bullets.push({ ... }) adds a bullet object to the end of the list: at the nose, with the ship's velocity plus the bullet speed, and a life of 55 frames.
bullets = [] at the bottom starts with an empty list.

Your turn

Under MAX_SPEED write the two bullet constants; under let ship write let bullets.
Above the keydown listener write shoot, followed by an empty line.
At the bottom, above resetShip(), write bullets = [].

Skills: Arrays and objects, Velocity and gravity

← Around the screen Fire! →

All steps