var Game = function(args) {
  this.player = args.player,
  this.score = 0,
  this.over = false
}

Game.prototype.spawnEnemy = function(){
  if(!this.over){
    var enemy = createElement("enemy", 1000, 350 * Math.random());
    moveElement(enemy, enemyRefresh, enemyLeft, 1000);
    setTimeout(this.spawnEnemy.bind(this), 500);
  }
}

Game.prototype.start = function(){
  document.getElementById("start").style.display = 'none';
  newPlayer.move();
  newPlayer.shoot();
  newGame.spawnEnemy();
  setInterval(collisionDetect, 10);
}

var Game = function(args) {
  this.player = args.player,
  this.score = 0,
  this.over = false
}

Game.prototype.spawnEnemy = function(){
  if(!this.over){
    var enemy = createElement("enemy", 1000, 350 * Math.random());
    moveElement(enemy, enemyRefresh, enemyLeft, 1000);
    setTimeout(this.spawnEnemy.bind(this), 1500);
  }
}

Game.prototype.start = function(){
  document.getElementById("start").style.display = 'none';
  newPlayer.move();
  newPlayer.shoot();
  newGame.spawnEnemy();
  setInterval(collisionDetect, 10);
}

change the enemy spawn time