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var _stage = new createjs.Stage("canvas");
_stage.canvas.style.border = "1px solid #000";
_stage.canvas.width = 800;
_stage.canvas.height = 600;

var _enemies = [];
var _enemyShots = [];
var _enemySize = 16;
var _enemyShotSize = {
    width: 2,
    height: 8
};
var _enemyOffsetX = _enemySize * 24;
var _enemyRows = 8;
var _enemyDirectionX = 1;
var _enemyShotNumber = 0;
var _enemyShotSpeed = 3;

var _player;
var _playerShots = [];
var _playerShotSize = {
    width: 4,
    height: 12
};
var _playerSize = 24;
var _playerCanMove = false;
var _playerSpeed = 4;
var _playerShotNumber = 0;
var _playerShotSpeed = 4;
var _playerLives;
var _playerLivesSprites = [];

var _offStage = -1000;

function randomRange(min, max) {
    return Math.floor(Math.random() * (max - min + 1)) + min;
}

function drawRect(x, y, width, height, color) {
    var rect = new createjs.Shape();
    rect.graphics
        .beginFill(color)
        .drawRect(0, 0, width, height)
        .endFill();
    rect.setBounds(0, 0, width, height);
    rect.x = x;
    rect.y = y;
    return rect;
}

function setPlayerLives(reset) {
    reset = (reset) ? reset : false;
    var x = _stage.canvas.width - _playerSize;
    var y = _stage.canvas.height - _playerSize;
    for (var i = 0; i < _playerLives; i++) {
        var size = _playerSize / 4;
        var r;
        if (reset) {
            r = _playerLivesSprites[i];
        } else {
            r = drawRect(0, 0, size, size, '#00f');
        }
        r.x = x - (i * _playerSize);
        r.y = y;
        if ( ! reset) {
            _playerLivesSprites.push(r);
            _stage.addChild(r);
        }
    }
}

function createEnemies(reset) {
    reset = (reset) ? reset : false;
    var area = _stage.canvas.width - _enemyOffsetX;
    var enemyBoxWidth = _enemySize + (_enemySize / 2);
    var numEnemies = Math.floor(area / enemyBoxWidth);
    for (var j = 0; j < _enemyRows; j++) {
        var y = _enemySize + (j * enemyBoxWidth);
        for (var i = 0; i < numEnemies; i++) {
            var r;
            if (reset) {
                var offset = numEnemies * j;
                var index = (j > 0) ? i + offset : i;
                r = _enemies[index];
            } else {
                r = drawRect(0, 0, _enemySize, _enemySize, '#000');
            }
            var x = _enemySize + (i * enemyBoxWidth);
            r.x = x;
            r.y = y;
            r.active = true;
            if ( ! reset) {
                _enemies.push(r);
                _stage.addChild(r);
            }
        }
    }
}

function createPlayer(reset) {
    reset = (reset) ? reset : false;
    if ( ! reset) {
        _player = drawRect(
            0,
            0,
            _playerSize,
            _playerSize,
            '#00f'
        );
    }
    _player.x = _stage.canvas.width / 2 - _playerSize / 2;
    _player.y = _stage.canvas.height - _playerSize * 2;
    _player.active = true;
    _playerLives = 3;
    if ( ! reset) {
        _stage.addChild(_player);
    }
}

function createShots(reset) {
    reset = (reset) ? reset : false;
    for (var i = 0; i < _enemies.length * 5; i++) {
        var r;
        if (reset) {
            r = _enemyShots[i];
        } else {
            r = drawRect(0, 0, _enemyShotSize.width, _enemyShotSize.height, '#f00');
        }
        r.x = _offStage;
        r.y = _offStage;
        r.active = false;
        
        if ( ! reset) {
            r.shotType = 'enemy';
            _enemyShots.push(r);
            _stage.addChild(r);
        }
    }
    
    for (var i = 0; i < 100; i++) {
        var r;
        if (reset) {
            r = _playerShots[i];
        } else {
            r = drawRect(0, 0, _playerShotSize.width, _playerShotSize.height, '#fa0')
        }
        r.x = _offStage;
        r.y = _offStage;
        r.active = false;
        
        if ( ! reset) {
            r.shotType = 'player';
            _playerShots.push(r);
            _stage.addChild(r);
        }
    }
}

function moveEnemies() {
    var enemyXMax = 0;
    var enemyXMin = Infinity;
    for (var i = 0; i < _enemies.length; i++) {
        var enemy = _enemies[i];
        if (enemy.active) {
            enemyXMax = (enemy.x > enemyXMax) ? enemy.x : enemyXMax;
            enemyXMin = (enemy.x < enemyXMin) ? enemy.x : enemyXMin;
            enemy.x += _enemyDirectionX;
        }
    }
    var XMin = _enemySize;
    var XMax = _stage.canvas.width - (_enemySize * 2);
    if (enemyXMax > XMax && _enemyDirectionX > 0) {
        _enemyDirectionX *= -1;
    } else if(enemyXMin < XMin && _enemyDirectionX < 0) {
        _enemyDirectionX = Math.abs(_enemyDirectionX);
    }
}

function movePlayer(e) {
    if (e) {
        if (e.type == 'mouseenter') {
            _playerCanMove = true;
        } else if (e.type == 'mouseleave') {
            _playerCanMove = false;
        }
    }
    
    if (_playerCanMove) {
        if (_stage.mouseX - _playerSize > _player.x) {
            _player.x += _playerSpeed;
        } else if (_stage.mouseX < _player.x) {
            _player.x -= _playerSpeed;
        }
    }
}

function moveShots() {
    for (var i = 0; i < _enemyShots.length; i++) {
        var shot = _enemyShots[i];
        if (shot.active) {
            shot.y += _enemyShotSpeed;
        }
        
        if (shot.y > _stage.canvas.height && shot.active) {
            shot.active = false;
            shot.x = _offStage;
            shot.y = _offStage;
        }
    }
    
    for (var i = 0; i < _playerShots.length; i++) {
        var shot = _playerShots[i];
        if (shot.active) {
            shot.y -= _playerShotSpeed;
        }
        
        if (shot.y < -_playerShotSize.height && shot.active) {
            shot.active = false;
            shot.x = _offStage;
            shot.y = _offStage;
        }
    }
}

function getActiveEnemies() {
    var activeEnemies = [];
    
    for (var i = 0; i < _enemies.length; i++) {
        var enemy = _enemies[i];
        if (enemy.active) {
            activeEnemies.push(enemy);
        }
    }
    
    return activeEnemies;
}

function fireEnemyShot() {
    var activeEnemies = getActiveEnemies();
    
    if (activeEnemies.length > 0) {
        var min = 0;
        var max = activeEnemies.length - 1;
        var random = randomRange(min, max);
        var enemy = activeEnemies[random];
        var shot = _enemyShots[_enemyShotNumber];
        shot.active = true;
        shot.x = enemy.x;
        shot.y = enemy.y;
        _enemyShotNumber++;
        if (_enemyShotNumber > _enemyShots.length - 1) {
            _enemyShotNumber = 0;
        }
    }
}

function firePlayerShot() {
    if (_player.active) {
         var shot = _playerShots[_playerShotNumber];
        shot.active = true;
        shot.x = _player.x;
        shot.y = _player.y;
        _playerShotNumber++;
        if (_playerShotNumber > _playerShots.length - 1) {
            _playerShotNumber = 0;
        }
    }
}

function intersect(shape1, shape2) {
    if (shape1.active == false || shape2.active == false) {
        return false;
    }
    
    if (
        shape1.x > 0 &&
        shape1.y > 0 &&
        shape2.x > 0 &&
        shape2.y > 0
    ) {
        var leftMost = (shape1.x < shape2.x) ? shape1 : shape2;
        var rightMost = (shape1.x > shape2.x) ? shape1 : shape2;
        var upMost = (shape1.y < shape2.y) ? shape1 : shape2;
        var downMost = (shape1.y > shape2.y) ? shape1 : shape2;
        
        var upperLeft = [rightMost.x, downMost.y];
        var upperRight = [leftMost.x + leftMost._bounds.width, downMost.y];
        var lowerLeft = [rightMost.x, upMost.y + upMost._bounds.height];
        var lowerRight = [leftMost.x + leftMost._bounds.width, upMost.y + upMost._bounds.height];
        
        var x = upperLeft[0];
        var y = upperLeft[1];
        
        var width = upperRight[0] - upperLeft[0];
        var height = lowerLeft[1] - upperLeft[1];
        
        if (width < 0 || height < 0) {
            width = 0;
            height = 0;
        }
    
        var area = width * height;
        
        return area > 0;
    }
    return false;
}

function collision() {
    for (var i = 0; i < _enemyShots.length; i++) {
        var shot = _enemyShots[i];
        if (intersect(shot, _player)) {
            shot.active = false;
            shot.x = _offStage;
            shot.y = _offStage;
            
            _playerLives--;
            var life = _playerLivesSprites[_playerLives];
            life.x = _offStage;
            life.y = _offStage;
            if (_playerLives <= 0) {
                _player.active = false;
            }
        }
    }
    
    for (var i = 0; i < _playerShots.length; i++) {
        var shot = _playerShots[i];
        for (var j = 0; j < _enemies.length; j++) {
            var enemy = _enemies[j];
            if (intersect(shot, enemy)) {
                shot.active = enemy.active = false;
                shot.x = enemy.x = _offStage;
                shot.y = enemy.y = _offStage;
            }
        }
    }
}

function reset() {
    init(true);
}

function init(reset) {
    reset = (reset) ? reset : false;
    createEnemies(reset);
    createPlayer(reset);
    setPlayerLives(reset);
    createShots(reset);
}

function update(e) {
    var activeEnemies = getActiveEnemies();
    
    if (activeEnemies.length == 0 || _playerLives <= 0) {
        reset();
    } else {
        moveEnemies();
        movePlayer();
        moveShots();
        collision();
    }
    _stage.update();
}

setInterval(fireEnemyShot, 750);
setInterval(firePlayerShot, 250);

_stage.addEventListener('mouseleave', movePlayer);
_stage.addEventListener('mouseenter', movePlayer);

createjs.Ticker.addEventListener('tick', update);
createjs.Ticker.setFPS(60);

init();

<canvas id="canvas"></canvas>