invaders/javascripts/game.js

var game = new Phaser.Game(1024, 576, Phaser.AUTO, 'game', { preload: preload, create: create, update: update });

function preload () {
  game.load.image('ship', 'images/ship.png');
  game.load.image('bullet', 'images/bullet.png');
  game.load.image('alien', 'images/alien.png');
  game.load.image('bomb', 'images/bomb.png');
}

var bulletTime = 0;

function create () {
  game.physics.startSystem(Phaser.Physics.ARCADE);

  // Initialize player
  player = game.add.sprite(512, 540, 'ship');
  player.anchor.setTo(0.5, 0.5);
  game.physics.enable(player, Phaser.Physics.ARCADE);

  player.body.bounce.x = 0.5;
  player.body.collideWorldBounds = true;

  // Initialize bullets
  bullets = game.add.group();
  bullets.enableBody = true;
  bullets.physicsBodyType = Phaser.Physics.ARCADE;
  bullets.createMultiple(3, 'bullet');
  bullets.setAll('anchor.x', 0.5);
  bullets.setAll('anchor.y', 1);
  bullets.setAll('checkWorldBounds', true);
  bullets.setAll('outOfBoundsKill', true);

  // Initialize aliens
  aliens = game.add.group();
  aliens.enableBody = true;
  aliens.physicsBodyType = Phaser.Physics.ARCADE;

  createAliens();

  // Initialize bombs
  bombs = game.add.group();
  bombs.enableBody = true;
  bombs.physicsBodyType = Phaser.Physics.ARCADE;
  bombs.createMultiple(10, 'bomb');
  bombs.setAll('anchor.x', 0.5);
  bombs.setAll('anchor.y', 0.5);
  bombs.setAll('checkWorldBounds', true);
  bombs.setAll('outOfBoundsKill', true);

  // Setup controls
  cursors = game.input.keyboard.createCursorKeys();
  fireButton = game.input.keyboard.addKey(Phaser.Keyboard.SPACEBAR);
}

function update () {
  playerMovement();

  // Firing?
  if (fireButton.isDown && player.alive) {
    fireBullet();
  }

  // Handle aliens dropping bombs
  handleBombs();

  game.physics.arcade.overlap(bullets, aliens, bulletHitsAlien, null, this);
  game.physics.arcade.overlap(bombs, player, bombHitsPlayer, null, this);
}

function playerMovement () {
  var maxVelocity = 500;

  if (cursors.left.isDown && player.body.velocity.x > -maxVelocity) {
    // Move to the left
    player.body.velocity.x -= 20;
  }
  else if (cursors.right.isDown && player.body.velocity.x < maxVelocity) {
    // Move to the right
    player.body.velocity.x += 20;
  }
  else {
    // Slow down
    if (player.body.velocity.x > 0) {
      player.body.velocity.x -= 4;
    }
    else if (player.body.velocity.x < 0) {
      player.body.velocity.x += 4;
    }
  }
}

function fireBullet () {
  if (game.time.now > bulletTime) {
    bullet = bullets.getFirstExists(false);

    if (bullet) {
      // And fire it
      bullet.reset(player.x, player.y - 16);
      bullet.body.velocity.y = -400;
      bullet.body.velocity.x = player.body.velocity.x / 4
      bulletTime = game.time.now + 500;
    }
  }
}

function bulletHitsAlien (bullet, alien) {
  bullet.kill();
  alien.kill();
}

function bombHitsPlayer (bomb, player) {
  bomb.kill();
  player.kill();
}

function createAliens () {
  for (var y = 0; y < 4; y++) {
    for (var x = 0; x < 10; x++) {
      var alien = aliens.create(x * 75, y * 50, 'alien');
      alien.anchor.setTo(0.5, 0.5);
      alien.body.moves = false;
    }
  }

  aliens.x = 64;
  aliens.y = 50;

  // All this does is basically start the invaders moving. Notice we're moving the Group they belong to, rather than the invaders directly.
  var tween = game.add.tween(aliens).to( { x: 284 }, 2500, Phaser.Easing.Sinusoidal.InOut, true, 0, 1000, true);

  // When the tween loops it calls descend
  tween.onLoop.add(descend, this);
}

function handleBombs () {
  aliens.forEachAlive(function (alien) {
    chanceOfDroppingBomb = game.rnd.integerInRange(0, 1000);
    if (chanceOfDroppingBomb == 0) {
      dropBomb(alien);
    }
  }, this)
}

function dropBomb (alien) {
  bomb = bombs.getFirstExists(false);

  if (bomb) {

    // And drop it
    bomb.reset(alien.x + aliens.x, alien.y + aliens.y + 16);
    bomb.body.velocity.y = +100;
    bomb.body.gravity.y = 250
  }
}

function descend () { aliens.y += 8; }